fixes #7002; fixes #17602; disallow using an object allocated on the stack for dynamic dispatch

[ringabout]

fixes #7002; fixes #17602

It causes undefined behaviors with ORC since objectAssignmentDefect is disabled for ORC

See also #7002 (comment)

Checked with

import strutils

type
    BaseObj = object of RootRef
      id: int
    DerivedObj = object of BaseObj
      name: float
      id2: int

method `$`(bo: BaseObj): string {.base.} =
    echo (bo.id)
    return "Base"

method `$`(dob: DerivedObj): string =
    echo (dob.id, dob.name, dob.id2)
    return "Derived"

type Container = object
    inner: BaseObj

proc foo =
  var
      dob = DerivedObj(id: 12, name: 1.23, id2: 5)
      cont = Container(inner: dob)
      dob2 = BaseObj()

  echo (dob, cont, dob2)

  echo (dob, cont, dob2)

  dob2 = dob

  echo (dob, cont, dob2)

foo()