KT-64385 Enable K2 KAPT by default

Also adds support for front-end compiler plugins in Kapt

plugins/kapt3/kapt3-cli/testData/integration/kotlinFileGeneration/build.txt

@@ -6,6 +6,7 @@ output/sources
 output/kotlin-sources
 
 # kotlinc
+-language-version 1.9
 -cp %KOTLIN_STDLIB%
 -d output/ap
 ap/Processor.kt
@@ -15,6 +16,7 @@ ap/META-INF/services/javax.annotation.processing.Processor
 output/ap/META-INF/services/javax.annotation.processing.Processor
 
 # kapt
+-language-version 1.9
 -Kapt-stubs=output/stubs
 -Kapt-classes=output/classes
 -Kapt-sources=output/sources