[KAPT4] KT-51982 Implement Kapt4AnalysisHandlerExtension, add KAPT CLI and Gradle IT

Co-authored-by: Alexander Udalov <Alexander.Udalov@jetbrains.com>

compiler/cli/src/org/jetbrains/kotlin/cli/common/arguments.kt

@@ -77,7 +77,10 @@ private fun switchToFallbackModeIfNecessary(arguments: CommonCompilerArguments,
             arguments.skipPrereleaseCheck = true
             arguments.allowUnstableDependencies = true
         }
-        arguments.useKapt4 && !isK2 -> warn("-Xuse-kapt4 flag can be only used with language version 2.0+.")
+        arguments.useKapt4 -> warn(
+            if (isK2) "Kapt 4 is an experimental feature. Use with caution."
+            else "-Xuse-kapt4 flag can be only used with language version 2.0+."
+        )
     }
 }