Update KotlinClassInnerStuffCache implementation

'KotlinClassInnerStuffCache' was copy-pasted from the platform's
'ClassInnerStuffCache' several years ago. After J2K and other changes,
it became quite dirty.

Besides cleaning things up, enum synthetic method handling have
significantly improved. Before, such methods were handled only in
'processDeclarationsInEnum', and 'getMethods()' didn't return them.
This led to inconsistent behavior and was reason for providing special
ad-hoc support in '1b6ded600518176b21cc308ed3e032ef8d04cc90'.

compiler/testData/asJava/ultraLightClasses/inlineClasses.java

@@ -4,6 +4,12 @@ public final class UInt /* UInt*/ {
 public enum Foo /* Foo*/ {
   ;
 
+  @org.jetbrains.annotations.NotNull()
+  public static Foo valueOf(@org.jetbrains.annotations.NotNull() java.lang.String) throws java.lang.IllegalArgumentException;//  valueOf(java.lang.String)
+
+  @org.jetbrains.annotations.NotNull()
+  public static Foo[] values();//  values()
+
   public final int getX();//  getX()
 
 }