Provide correct type names for unresolved types instead of error.UnresolvedCla$$

[Jeffset]

Currently Yatagan yields fake error.UnresolvedCla$$ stub name for every unresolved type. This is the case for both KSP and KAPT.

This is the uniformized behavior introduced because:

1. KSP doesn't provide real unresolved type name at all, only generic <ERROR TYPE> string can be obtained
2. KAPT requires correctErrorTypes option to be set, otherwise it provides error.NonExistentClass.

So, Yatagan detects those cases and provides error.UnresolvedCla$$ for every backend.

But this is really not an acceptable behavior, as sometimes there's no way to identify what types are actually missing/unresolved, if they are not used in hand-written code though are missing from the compilation classpath (typically when users use implementation instead of api in Gradle).

So there's actually several problems here:

1. No names for unresolved/missing types at all.
2. Yatagan doesn't explicitly check for error types in graphs, and may even be able to generate code with them. The code will then fail to compile, leaving the user with syntactic errors concerning error.UnresolvedCla$$ and with no info on what those types actually are and from where they are referenced from.

In order to support error type names in KSP, the google/ksp#1232 needs to be resolved first.
Support from the KAPT backend can be added already, but there's no way to test this, as correctErrorTypes option is inaccessible in room-compile-testing, so the issue https://issuetracker.google.com/u/2/issues/248552462 has to be resolved for that.

Yatagan error types detection can (and should) be implemented now, nothing blocks it.

1. Implement error type detection in validation pipeline (in order to provide the user with the info on where the unresolved types are referenced)
2. Maybe implement correct error types with KAPT backend (no test coverage possible though?)
3. Wait for KSP support for error type names and add it later.