An optimizer for ARC (#14962)

* WIP: an optimizer for ARC
* do not optimize away destructors in 'finally' if unstructured control flow is involved
* optimized the optimizer
* minor code cleanup
* first steps to .cursor inference
* cursor inference: big steps to a working solution
* baby steps
* better .cursor inference
* new feature: expandArc for easy inspection of the AST after ARC transformations
* added topt_cursor test
* adapt tests
* cleanups, make tests green
* optimize common traversal patterns
* moved test case
* fixes .cursor inference so that npeg compiles once again
* cursor inference: more bugfixes

Co-authored-by: Clyybber <darkmine956@gmail.com>

tests/casestmt/t12785.nim

@@ -1,49 +0,0 @@
-discard """
-  cmd: '''nim c --newruntime $file'''
-  output: '''copied
-copied
-2
-destroyed
-destroyed
-copied
-copied
-2
-destroyed
-destroyed'''
-"""
-
-type
-  ObjWithDestructor = object
-    a: int
-proc `=destroy`(self: var ObjWithDestructor) =
-  echo "destroyed"
-
-proc `=`(self: var ObjWithDestructor, other: ObjWithDestructor) =
-  echo "copied"
-
-proc test(a: range[0..1], arg: ObjWithDestructor) =
-  var iteration = 0
-  while true:
-    {.computedGoto.}
-
-    let
-      b = int(a) * 2
-      c = a
-      d = arg
-      e = arg
-
-    discard c
-    discard d
-    discard e
-
-    inc iteration
-
-    case a
-    of 0:
-      assert false
-    of 1:
-      echo b
-      if iteration == 2:
-        break
-
-test(1, ObjWithDestructor())