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

plugins/kapt3/kapt3-compiler/testData/converter/kt17567.kt

@@ -4,3 +4,8 @@ internal class MutableEntry<K, V>(
         private val internal: MutableMap<K, V>,
         override val key: K, value: V
 ): MutableMap.MutableEntry<K, V>
+
+// <K:Ljava/lang/Object;V:Ljava/lang/Object;>
+// Ljava/lang/Object;
+// Ljava/util/Map$Entry<TK;TV;>;
+// Lkotlin/jvm/internal/markers/KMutableMap$Entry;