Stub generation infrastructure (except for metadata generation) for KAPT+K2

This commit includes the basic Java stubs generation infrastructure and
the corresponding tests. The main entry point is called
Kapt4StubGenerator. Calls to it from production code will be added in a
separate commit.

 #KT-51982

generators/tests/org/jetbrains/kotlin/generators/tests/GenerateTests.kt

@@ -38,6 +38,7 @@ import org.jetbrains.kotlin.kapt3.test.runners.AbstractClassFileToSourceStubConv
 import org.jetbrains.kotlin.kapt3.test.runners.AbstractIrClassFileToSourceStubConverterTest
 import org.jetbrains.kotlin.kapt3.test.runners.AbstractIrKotlinKaptContextTest
 import org.jetbrains.kotlin.kapt3.test.runners.AbstractKotlinKaptContextTest
+import org.jetbrains.kotlin.kapt4.AbstractKotlinKapt4ContextTest
 import org.jetbrains.kotlin.lombok.*
 import org.jetbrains.kotlin.noarg.*
 import org.jetbrains.kotlin.parcelize.test.runners.*
@@ -385,6 +386,11 @@ fun main(args: Array<String>) {
                 model("converter")
             }
         }
+        testGroup("plugins/kapt4/tests-gen", "plugins/kapt4/") {
+            testClass<AbstractKotlinKapt4ContextTest> {
+                model("../kapt3/kapt3-compiler/testData/converter")
+            }
+        }
 
         testGroup("plugins/assign-plugin/tests-gen", "plugins/assign-plugin/testData") {
             testClass<AbstractAssignmentPluginDiagnosticTest> {