[perf] `FlutterInitializer.edtInitialization`: get slow actions off the EDT

Recent test runs produce at least two places where `FlutterInitializer.edtInitialization` is over-burdening the EDT:

```
java.lang.Throwable: Slow operations are prohibited on EDT. See SlowOperations.assertSlowOperationsAreAllowed javadoc.
at com.intellij.openapi.diagnostic.Logger.error(Logger.java:375)
at com.intellij.util.SlowOperations.logError(SlowOperations.java:172)
at com.intellij.util.SlowOperations.assertSlowOperationsAreAllowed(SlowOperations.java:120)
at com.intellij.openapi.vfs.newvfs.persistent.FSRecordsImpl.update(FSRecordsImpl.java:760)
at com.intellij.openapi.vfs.newvfs.persistent.PersistentFSImpl.findChildInfo(PersistentFSImpl.java:631)
at com.intellij.openapi.vfs.newvfs.impl.VirtualDirectoryImpl.findInPersistence(VirtualDirectoryImpl.java:155)
at com.intellij.openapi.vfs.newvfs.impl.VirtualDirectoryImpl.doFindChild(VirtualDirectoryImpl.java:138)
at com.intellij.openapi.vfs.newvfs.impl.VirtualDirectoryImpl.findChild(VirtualDirectoryImpl.java:84)
at com.intellij.openapi.vfs.newvfs.impl.VirtualDirectoryImpl.findChild(VirtualDirectoryImpl.java:573)
at com.intellij.openapi.vfs.newvfs.impl.VirtualDirectoryImpl.findChild(VirtualDirectoryImpl.java:48)
at com.intellij.openapi.vfs.newvfs.VfsImplUtil.findFileByPath(VfsImplUtil.java:56)
at com.intellij.openapi.vfs.impl.local.LocalFileSystemBase.findFileByPath(LocalFileSystemBase.java:57)
at com.intellij.openapi.vfs.impl.VirtualFileManagerImpl.findByUrl(VirtualFileManagerImpl.java:384)
at com.intellij.openapi.vfs.impl.VirtualFileManagerImpl.findFileByUrl(VirtualFileManagerImpl.java:371)
at com.intellij.workspaceModel.ide.impl.VirtualFileUrlBridge.findVirtualFile(VirtualFileUrlBridge.kt:41)
at com.intellij.workspaceModel.ide.impl.VirtualFileUrlBridge.getFile(VirtualFileUrlBridge.kt:18)
at com.intellij.workspaceModel.ide.impl.legacyBridge.module.ModuleBridgeImpl.getModuleFile(ModuleBridgeImpl.kt:56)
at io.flutter.FlutterInitializer.edtInitialization(FlutterInitializer.java:177)
at io.flutter.FlutterInitializer.lambda$executeProjectStartup$1(FlutterInitializer.java:148)
at com.intellij.openapi.application.impl.NonBlockingReadActionImpl$Submission.lambda$safeTransferToEdt$6(NonBlockingReadActionImpl.java:752)
at com.intellij.openapi.application.TransactionGuardImpl.runWithWritingAllowed(TransactionGuardImpl.java:240)
at com.intellij.openapi.application.TransactionGuardImpl.access$100(TransactionGuardImpl.java:26)
at com.intellij.openapi.application.TransactionGuardImpl$1.run(TransactionGuardImpl.java:202)
at com.intellij.openapi.application.impl.AppImplKt$runnableUnitFunction$1.invoke(appImpl.kt:104)
at com.intellij.openapi.application.impl.AppImplKt$runnableUnitFunction$1.invoke(appImpl.kt:104)
at com.intellij.platform.locking.impl.NestedLocksThreadingSupport.doRunWriteIntentReadAction(NestedLocksThreadingSupport.kt:666)
at com.intellij.platform.locking.impl.NestedLocksThreadingSupport.runPreventiveWriteIntentReadAction(NestedLocksThreadingSupport.kt:640)
at com.intellij.platform.locking.impl.NestedLocksThreadingSupport.runWriteIntentReadAction(NestedLocksThreadingSupport.kt:633)
at com.intellij.openapi.application.impl.ApplicationImpl.runIntendedWriteActionOnCurrentThread(ApplicationImpl.java:1022)
at com.intellij.openapi.application.impl.ApplicationImpl$7.run(ApplicationImpl.java:587)
at com.intellij.openapi.application.impl.FlushQueue.runNextEvent(FlushQueue.java:122)
at com.intellij.openapi.application.impl.FlushQueue.flushNow(FlushQueue.java:43)
at java.desktop/java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.desktop/java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.desktop/java.awt.EventQueue$4.run(Unknown Source)
at java.desktop/java.awt.EventQueue$4.run(Unknown Source)
at java.base/java.security.AccessController.doPrivileged(Unknown Source)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.desktop/java.awt.EventQueue.dispatchEvent(Unknown Source)
at com.intellij.ide.IdeEventQueue.defaultDispatchEvent(IdeEventQueue.kt:595)
at com.intellij.ide.IdeEventQueue._dispatchEvent(IdeEventQueue.kt:488)
at com.intellij.ide.IdeEventQueue.dispatchEvent$lambda$12$lambda$11$lambda$10$lambda$9(IdeEventQueue.kt:313)
at com.intellij.openapi.progress.impl.CoreProgressManager.computePrioritized(CoreProgressManager.java:865)
at com.intellij.ide.IdeEventQueue.dispatchEvent$lambda$12$lambda$11$lambda$10(IdeEventQueue.kt:312)
at com.intellij.ide.IdeEventQueueKt.performActivity$lambda$3(IdeEventQueue.kt:974)
at com.intellij.openapi.application.TransactionGuardImpl.performActivity(TransactionGuardImpl.java:110)
at com.intellij.ide.IdeEventQueueKt.performActivity(IdeEventQueue.kt:974)
at com.intellij.ide.IdeEventQueue.dispatchEvent$lambda$12(IdeEventQueue.kt:307)
at com.intellij.ide.IdeEventQueue.dispatchEvent(IdeEventQueue.kt:347)
at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.desktop/java.awt.EventDispatchThread.run(Unknown Source)
```

and

```
java.lang.Throwable: Slow operations are prohibited on EDT. See SlowOperations.assertSlowOperationsAreAllowed javadoc.
at com.intellij.openapi.diagnostic.Logger.error(Logger.java:375)
at com.intellij.util.SlowOperations.logError(SlowOperations.java:172)
at com.intellij.util.SlowOperations.assertSlowOperationsAreAllowed(SlowOperations.java:120)
at com.intellij.openapi.vfs.newvfs.persistent.FSRecordsImpl.update(FSRecordsImpl.java:760)
at com.intellij.openapi.vfs.newvfs.persistent.PersistentFSImpl.findChildInfo(PersistentFSImpl.java:631)
at com.intellij.openapi.vfs.newvfs.impl.VirtualDirectoryImpl.findInPersistence(VirtualDirectoryImpl.java:155)
at com.intellij.openapi.vfs.newvfs.impl.VirtualDirectoryImpl.doFindChild(VirtualDirectoryImpl.java:138)
at com.intellij.openapi.vfs.newvfs.impl.VirtualDirectoryImpl.findChild(VirtualDirectoryImpl.java:84)
at com.intellij.openapi.vfs.newvfs.impl.VirtualDirectoryImpl.findChild(VirtualDirectoryImpl.java:573)
at com.intellij.openapi.vfs.newvfs.impl.VirtualDirectoryImpl.findChild(VirtualDirectoryImpl.java:48)
at io.flutter.module.FlutterModuleBuilder.findEmbeddedModuleFile(FlutterModuleBuilder.java:249)
at io.flutter.module.FlutterModuleBuilder.addAndroidModule(FlutterModuleBuilder.java:190)
at io.flutter.FlutterInitializer.edtInitialization(FlutterInitializer.java:185)
at io.flutter.FlutterInitializer.lambda$executeProjectStartup$1(FlutterInitializer.java:148)
at com.intellij.openapi.application.impl.NonBlockingReadActionImpl$Submission.lambda$safeTransferToEdt$6(NonBlockingReadActionImpl.java:752)
at com.intellij.openapi.application.TransactionGuardImpl.runWithWritingAllowed(TransactionGuardImpl.java:240)
at com.intellij.openapi.application.TransactionGuardImpl.access$100(TransactionGuardImpl.java:26)
at com.intellij.openapi.application.TransactionGuardImpl$1.run(TransactionGuardImpl.java:202)
at com.intellij.openapi.application.impl.AppImplKt$runnableUnitFunction$1.invoke(appImpl.kt:104)
at com.intellij.openapi.application.impl.AppImplKt$runnableUnitFunction$1.invoke(appImpl.kt:104)
at com.intellij.platform.locking.impl.NestedLocksThreadingSupport.doRunWriteIntentReadAction(NestedLocksThreadingSupport.kt:666)
at com.intellij.platform.locking.impl.NestedLocksThreadingSupport.runPreventiveWriteIntentReadAction(NestedLocksThreadingSupport.kt:640)
at com.intellij.platform.locking.impl.NestedLocksThreadingSupport.runWriteIntentReadAction(NestedLocksThreadingSupport.kt:633)
at com.intellij.openapi.application.impl.ApplicationImpl.runIntendedWriteActionOnCurrentThread(ApplicationImpl.java:1022)
at com.intellij.openapi.application.impl.ApplicationImpl$7.run(ApplicationImpl.java:587)
at com.intellij.openapi.application.impl.FlushQueue.runNextEvent(FlushQueue.java:122)
at com.intellij.openapi.application.impl.FlushQueue.flushNow(FlushQueue.java:43)
at java.desktop/java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.desktop/java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.desktop/java.awt.EventQueue$4.run(Unknown Source)
at java.desktop/java.awt.EventQueue$4.run(Unknown Source)
at java.base/java.security.AccessController.doPrivileged(Unknown Source)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.desktop/java.awt.EventQueue.dispatchEvent(Unknown Source)
at com.intellij.ide.IdeEventQueue.defaultDispatchEvent(IdeEventQueue.kt:595)
at com.intellij.ide.IdeEventQueue._dispatchEvent(IdeEventQueue.kt:488)
at com.intellij.ide.IdeEventQueue.dispatchEvent$lambda$12$lambda$11$lambda$10$lambda$9(IdeEventQueue.kt:313)
at com.intellij.openapi.progress.impl.CoreProgressManager.computePrioritized(CoreProgressManager.java:865)
at com.intellij.ide.IdeEventQueue.dispatchEvent$lambda$12$lambda$11$lambda$10(IdeEventQueue.kt:312)
at com.intellij.ide.IdeEventQueueKt.performActivity$lambda$3(IdeEventQueue.kt:974)
at com.intellij.openapi.application.TransactionGuardImpl.performActivity(TransactionGuardImpl.java:110)
at com.intellij.ide.IdeEventQueueKt.performActivity(IdeEventQueue.kt:974)
at com.intellij.ide.IdeEventQueue.dispatchEvent$lambda$12(IdeEventQueue.kt:307)
at com.intellij.ide.IdeEventQueue.dispatchEvent(IdeEventQueue.kt:347)
at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.desktop/java.awt.EventDispatchThread.run(Unknown Source)
```