[Deps] Investigate ways of integrating `ktfmt`

Nobody has claimed this yet.

We're vendoring `ktfmt` ([here](https://github.com/fwcd/ktfmt/tree/kls)) since it uses the embedded Kotlin compiler rather than the standard one, which we use. The embedded Kotlin compiler uses other package paths (e.g. `org.jetbrains.kotlin.com.intellij` instead of `com.intellij`), which causes weird clashes at runtime, for example:

```
java.lang.NoSuchMethodError: 'org.jetbrains.kotlin.cli.jvm.compiler.KotlinCoreEnvironment org.jetbrains.kotlin.cli.jvm.compiler.KotlinCoreEnvironment$Companion.createForProduction(org.jetbrains.kotlin.com.intellij.openapi.Disposable, org.jetbrains.kotlin.config.CompilerConfiguration, org.jetbrains.kotlin.cli.jvm.compiler.EnvironmentConfigFiles)'
at com.facebook.ktfmt.format.Parser.parse(Parser.kt:45)
at com.facebook.ktfmt.format.Formatter.sortedAndDistinctImports(Formatter.kt:141)
at com.facebook.ktfmt.format.Formatter.format(Formatter.kt:84)
at org.javacs.kt.formatting.FormatterKt.formatKotlinCode(Formatter.kt:10)
at org.javacs.kt.KotlinTextDocumentService$formatting$1.invoke(KotlinTextDocumentService.kt:204)
at org.javacs.kt.KotlinTextDocumentService$formatting$1.invoke(KotlinTextDocumentService.kt:199)
at org.javacs.kt.util.AsyncExecutor.compute$lambda-2(AsyncExecutor.kt:19)
at java.base/java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1700)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:829)
```

While this is non-ideal, it's currently the best solution I could find that works for our setup. A better solution would be to automate this as part of our Gradle build (i.e. rewrite the package paths and replace the transitive `kotlin-compiler-embeddable` dependency with `kotlin-compiler` - basically do [this](https://github.com/facebookincubator/ktfmt/compare/main...fwcd:kls) automatically), but I couldn't figure out a clean way of doing so yet.

_Originally posted by @fwcd in https://github.com/fwcd/kotlin-language-server/issues/330#issuecomment-1072499406_

---

... there were other dependencies which needed the non-embedded compiler and didn't have an embedded version themselves (I think it was the `kotlin-scripting-compiler` or perhaps the IDEA plugin, which we no longer depend on though, can't remember).

_Originally posted by @fwcd in https://github.com/fwcd/kotlin-language-server/issues/330#issuecomment-1073071615_

Start with the Gradle build and the linked ktfmt fork comparison; trace Parser.kt and Formatter.kt where the runtime clash appears. Investigate replacing kotlin-compiler-embeddable with kotlin-compiler and the package-path rewrite, including the unresolved non-embedded dependencies. Done means the integration avoids the reported NoSuchMethodError.

Written by the indexing model from the issue text.