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/errorSuperclass.fir.txt

@@ -0,0 +1,20 @@
+package test;
+
+@kotlin.Metadata()
+@java.lang.annotation.Retention(value = java.lang.annotation.RetentionPolicy.RUNTIME)
+public abstract @interface Anno {
+}
+
+////////////////////
+
+package test;
+
+@kotlin.Metadata()
+@Anno()
+@kotlin.Suppress(names = {"UNRESOLVED_REFERENCE"})
+public final class ClassWithParent extends Foo implements Bar, Baz, java.lang.CharSequence {
+
+    public ClassWithParent() {
+        super();
+    }
+}