[FIR] Change scheme of generating declarations by plugins

Methods `needToGenerateAdditionalMembersInClass` and
  `needToGenerateNestedClassifiersInClass` are removed, now compiler
  uses `get...Names` and `getTopLevel...` methods to determine which
  extension may generate declaration with specific classId/callableId

This is needed to simplify API of FirDeclarationGenerationExtension and
  provide guarantee that `generate...` method will be called with
  specific classId/callableId only if specific extensions returned name
  for this id from `getName...` functions

core/compiler.common/src/org/jetbrains/kotlin/name/FqNamesUtil.kt

@@ -75,3 +75,11 @@ fun <V> FqName.findValueForMostSpecificFqname(values: Map<FqName, V>): V? {
 
     return suitableItems.minByOrNull { (fqName, _) -> fqName.tail(this).asString().length }?.value
 }
+
+fun ClassId.callableIdForConstructor(): CallableId {
+    return if (isNestedClass) {
+        CallableId(outerClassId!!, shortClassName)
+    } else {
+        CallableId(packageFqName, shortClassName)
+    }
+}