Kapt: Do not use awkward ('$' -> '/') logic for KAPT3 class builder mode

So (for the most often reproduction case) #KT-19433 Fixed

Before this commit, internal names for nested classes were written as test/Foo/Bar (comparing to test/Foo$Bar in the normal mode), as getting qualified names from such internal names was trivial. But, because of IC, we needed to write class files to the disk, so our decompiler could find such "broken" classes and read it in a wrong way.

core/descriptor.loader.java/src/org/jetbrains/kotlin/load/kotlin/typeSignatureMapping.kt

@@ -47,8 +47,8 @@ private fun <T : Any> JvmTypeFactory<T>.boxTypeIfNeeded(possiblyPrimitiveType: T
         if (needBoxedType) boxType(possiblyPrimitiveType) else possiblyPrimitiveType
 
 interface TypeMappingConfiguration<out T : Any> {
-    companion object {
-        val DEFAULT_INNER_CLASS_NAME_FACTORY = fun(outer: String, inner: String) = outer + "$" + inner
+    private companion object {
+        private val DEFAULT_INNER_CLASS_NAME_FACTORY = fun(outer: String, inner: String) = outer + "$" + inner
     }
 
     val innerClassNameFactory: (outer: String, inner: String) -> String