Add support for KSP

[rossbacher]

Added support for KSP (https://github.com/google/ksp) via Rooms XProcessing library (https://github.com/androidx/androidx/tree/androidx-main/room/room-compiler-processing) as so we can still support kapt and java annotation processor.

Note: The tests are currently failing as there is a bug that causes issues with sub classes right now, still investigating this.

Few other changes:

• Migrated processor and all of it's tests to Kotlin.
• Move compile testing to https://github.com/tschuchortdev/kotlin-compile-testing/tree/master
• Move mocking to Mockk (https://mockk.io/)
• Add KTlint for processor (will add for other modules in separate PR)
• Removed some old dependencies and removed need to JCenter
• Added test library to show kapt setup.

[rossbacher]

Awesome - thanks for all the Koltin conversions, setting up ktlint and mockk! I'll take a look at the inner class error and see if I have any insight

@BenSchwab I created an issue ticket with ksp here https://github.com/google/ksp/issues/492 for the inner class error.