scoped memory management (#14790)

* fixes the regressions
* closes #13936
* scope based memory management implemented
* enabled tcontrolflow.nim test case
* final cleanups

tests/arc/tmovebug.nim

@@ -247,7 +247,7 @@ iterator combinations[T](s: openarray[T], k: int): seq[T] =
       break
 
 type
-  UndefEx = object of Exception
+  UndefEx = object of ValueError
 
 proc main2 =
   var delayedSyms = @[1, 2, 3]
@@ -318,10 +318,10 @@ proc `=sink`(dest: var O2, src: O2) =
 
 var testSeq: O2
 
-proc Update(): void =
+proc update() =
   # testSeq.add(0) # uncommenting this line fixes the leak
   testSeq = O2(s: @[])
   testSeq.s.add(0)
 
 for i in 1..3:
-  Update()
+  update()