enable refc with move analyzer

[ringabout]

ref #12340

[arnetheduck]

what's the status of this one? it's highly interesting as migration path from refc to orc, as it makes it easier to use the same code with both collectors.

[ringabout]

The problem is that refc cannot handle copying of upcast of subtypes. arc circumvents this issue by disabling ObjectAssignmentDefect.

[arnetheduck]

The problem is that refc cannot handle copying of upcast of subtypes

so what would be the steps from here? do you mean valid or invalid upcasts?

[ringabout]

I mean valid upcast now became illegal with this PR

type
  A {.inheritable.} = object
  B = object of A
    f: int

proc `=destroy`(x: var B) = discard


proc `$$`[T](x: sink T): string =
  "{}"

let a: ref A = new(B)
doAssert $$a[] == "{}"

it gives ObjectAssignmentDefect with this PR