FIR2IR: cache functions and their parents properly

compiler/testData/codegen/box/closures/extensionClosure.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 class Point(val x : Int, val y : Int)
 
 fun box() : String {

compiler/testData/codegen/box/closures/kt3738.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 class A {
     fun foo() {}
     fun bar(f: A.() -> Unit = {}) {}