Reconciler doesn't leverage --release option

In a project using a recent JDK (e.g., 23) that is configured with `--release 19`, the reconciler will see class files from the most recent version (here 23), despite the `--release` option.

Classes are read in this call stack:
```
ClassFileReader.(byte[], char[], boolean) line: 242
ClassFile.getJarBinaryTypeInfo() line: 228
ClassFile.existsUsingJarTypeCache() line: 147
NameLookup.seekTypesInBinaryPackage(String, IPackageFragment, boolean, int, IJavaElementRequestor) line: 1475
NameLookup.seekTypes(String, IPackageFragment, boolean, int, IJavaElementRequestor, boolean) line: 1442
NameLookup.findType(String, IPackageFragment, boolean, int, boolean, boolean) line: 988
NameLookup.findType(String, String, boolean, int, boolean, boolean, boolean, IProgressMonitor, IPackageFragmentRoot[]) line: 815
NameLookup.findType(String, String, boolean, int, boolean, IPackageFragmentRoot[]) line: 734
CancelableNameEnvironment(SearchableEnvironment).find(String, String, IPackageFragmentRoot[]) line: 191
CancelableNameEnvironment(SearchableEnvironment).findType(char[], char[][], char[]) line: 549
LookupEnvironment.fromSplitPackageOrOracle(IModuleAwareNameEnvironment, ModuleBinding, PackageBinding, char[]) line: 473
LookupEnvironment.lambda$1(IModuleAwareNameEnvironment, PackageBinding, char[], ModuleBinding) line: 346
0x00007f6213aac050.apply(Object) line: not available
LookupEnvironment.askForTypeFromModules(ModuleBinding, ModuleBinding[], Function) line: 440
```

While the `ClassFile` could use its enclosing `IJavaProject` to detect the `--release 19` option, we indirectly use `JRTUtil.getClassfileContent()` which constantly passes `null` as the `release` in `getJrtSystem()`. This, btw, seems the prevalent use of that method!

To observe this behavior, use the above project configuration and inside a method catching MalformedURLException type the following **without saving**:
```
URL.of(null, null);
```
You will not see an error **until the file is saved**. This demonstrates that in fact the 23 version is used by the reconciler, where the method exists (since 21).

Manually tweaking `getJrtSystem()` to use release "19" (in the debugger) does not suffice, because the logic used to locate the class file is in `JrtFileSystem.getClassfileContent()` / `JrtFileSystem.getFileBytes(String, String)`, which have no override in `JrtFileSystemWithOlderRelease`.

I'm not even sure if its a good idea to amend the code to respect the release version, because there's a lot of caching going on, where I don't readily see if those caches are multi-version aware??

In fact, I don't readily see if there is any low hanging fruit, or whether the inconsistency is actually tolerable in face of the complexity.