more arc improvements (#12690)

* ARC: bugfix for =destroy for inherited objects
* added code useful for debugging

tests/destructor/tlists.nim

@@ -1,79 +0,0 @@
-discard """
-  output: '''
-@[1, 2, 3]
-Success
-@["a", "b", "c"]
-0'''
-  cmd: '''nim c --gc:destructors $file'''
-"""
-
-import os
-import math
-import lists
-import strutils
-
-proc mkleak() =
-  # allocate 1 MB via linked lists
-  let numberOfLists = 100
-  for i in countUp(1, numberOfLists):
-    var leakList = initDoublyLinkedList[string]()
-    let numberOfLeaks = 5000
-    for j in countUp(1, numberOfLeaks):
-      leakList.append(newString(200))
-
-proc mkManyLeaks() =
-  for i in 0..0:
-    mkleak()
-  echo "Success"
-
-iterator foobar(c: string): seq[string] {.closure.} =
-  yield @["a", "b", c]
-
-proc tsimpleClosureIterator =
-  var myc = "c"
-  for it in foobar(myc):
-    echo it
-
-type
-  LazyList = ref object
-    c: proc() {.closure.}
-
-proc tlazyList =
-  let dep = @[1, 2, 3]
-  var x = LazyList(c: proc () = echo(dep))
-  x.c()
-
-type
-  Foo = ref object
-
-proc tleakingNewStmt =
-  var x: Foo
-  for i in 0..10:
-    new(x)
-
-iterator infinite(): int {.closure.} =
-  var i = 0
-  while true:
-    yield i
-    inc i
-
-iterator take(it: iterator (): int, numToTake: int): int {.closure.} =
-  var i = 0
-  for x in it():
-    if i >= numToTake:
-      break
-    yield x
-    inc i
-
-proc take3 =
-  for x in infinite.take(3):
-    discard
-
-let startMem = getOccupiedMem()
-take3()
-tlazyList()
-
-mkManyLeaks()
-tsimpleClosureIterator()
-tleakingNewStmt()
-echo getOccupiedMem() - startMem