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.

compiler/testData/codegen/kapt/interfaceImpls.txt

@@ -1,14 +1,14 @@
 @kotlin.Metadata
-public interface A {
-    inner class A/DefaultImpls
-    public abstract method a(): void
-    public abstract method b(): void
+public final class A$DefaultImpls {
+    inner class A$DefaultImpls
+    public static method a(p0: A): void
 }
 
 @kotlin.Metadata
-public final class A/DefaultImpls {
-    inner class A/DefaultImpls
-    public static method a(p0: A): void
+public interface A {
+    inner class A$DefaultImpls
+    public abstract method a(): void
+    public abstract method b(): void
 }
 
 @kotlin.Metadata