ARC: misc bugfixes (#13156)

* fixes #13102
* closes #13149
* ARC: fixes a move optimizer bug (there are more left regarding array and tuple indexing)
* proper fix; fixes #12957
* fixes yet another case object '=' code generation problem

tests/arc/tmovebug.nim

@@ -0,0 +1,64 @@
+discard """
+  cmd: "nim c --gc:arc $file"
+  output: '''5'''
+"""
+
+# move bug
+type
+  TMyObj = object
+    p: pointer
+    len: int
+
+var destroyCounter = 0
+
+proc `=destroy`(o: var TMyObj) =
+  if o.p != nil:
+    dealloc o.p
+    o.p = nil
+    inc destroyCounter
+
+proc `=`(dst: var TMyObj, src: TMyObj) =
+  `=destroy`(dst)
+  dst.p = alloc(src.len)
+  dst.len = src.len
+
+proc `=sink`(dst: var TMyObj, src: TMyObj) =
+  `=destroy`(dst)
+  dst.p = src.p
+  dst.len = src.len
+
+type
+  TObjKind = enum Z, A, B
+  TCaseObj = object
+    case kind: TObjKind
+    of Z: discard
+    of A:
+      x1: int # this int plays important role
+      x2: TMyObj
+    of B:
+      y: TMyObj
+
+proc use(a: TCaseObj) = discard
+
+proc moveBug(i: var int) =
+  var a: array[2, TCaseObj]
+  a[i] = TCaseObj(kind: A, x1: 5000, x2: TMyObj(len: 5, p: alloc(5))) # 1
+  a[i+1] = a[i] # 2
+  inc i
+  use(a[i-1])
+
+var x = 0
+moveBug(x)
+
+proc moveBug2(): (TCaseObj, TCaseObj) =
+  var a: array[2, TCaseObj]
+  a[0] = TCaseObj(kind: A, x1: 5000, x2: TMyObj(len: 5, p: alloc(5)))
+  a[1] = a[0] # can move 3
+  result[0] = TCaseObj(kind: A, x1: 5000, x2: TMyObj(len: 5, p: alloc(5))) # 4
+  result[1] = result[0] # 5
+
+proc main =
+  discard moveBug2()
+
+main()
+echo destroyCounter