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'.

analysis/decompiled/light-classes-for-decompiled/src/org/jetbrains/kotlin/analysis/decompiled/light/classes/KtLightClassForDecompiledDeclaration.kt

@@ -95,9 +95,6 @@ open class KtLightClassForDecompiledDeclaration(
         lastParent: PsiElement?,
         place: PsiElement
     ): Boolean {
-        if (isEnum) {
-            if (!KotlinClassInnerStuffCache.processDeclarationsInEnum(processor, state, myInnersCache)) return false
-        }
         return PsiClassImplUtil.processDeclarationsInClass(
             this, processor, state, null,
             lastParent, place, PsiUtil.getLanguageLevel(place), false

analysis/decompiled/light-classes-for-decompiled/src/org/jetbrains/kotlin/analysis/decompiled/light/classes/KtLightClassForDecompiledDeclarationBase.kt

@@ -4,8 +4,7 @@ package org.jetbrains.kotlin.analysis.decompiled.light.classes
 
 import com.intellij.psi.PsiClass
 import com.intellij.psi.PsiElement
-import com.intellij.psi.impl.source.PsiExtensibleClass
-import org.jetbrains.kotlin.asJava.classes.KtLightClass
+import org.jetbrains.kotlin.asJava.classes.KtExtensibleLightClass
 import org.jetbrains.kotlin.asJava.elements.KtLightElementBase
 import org.jetbrains.kotlin.psi.KtClassOrObject
 
@@ -13,4 +12,4 @@ abstract class KtLightClassForDecompiledDeclarationBase(
     override val clsDelegate: PsiClass,
     clsParent: PsiElement,
     final override val kotlinOrigin: KtClassOrObject?
-) : KtLightElementBase(clsParent), PsiClass, KtLightClass, PsiExtensibleClass
+) : KtLightElementBase(clsParent), PsiClass, KtExtensibleLightClass