fixes #25726; adds sink/var when match or type param

[demotomohiro]

No description provided.

[demotomohiro]

var T doesn't work with or type.
It can be fixed in the same way as this PR, but that fix can be breaking change(compiling tests/arc/trtree.nim fails).

Following code compiles without error because typeof(x) is evaluated to int:

proc test(x: var int): typeof(x) =
  var y: typeof(x)
  return y

var a = 1
echo test(a)

In following code, typeof(x) is int after test is instantiated.
But if I fixed the bug, typeof(x) becomes var int and generates compile error.

proc test(x: string or var int): typeof(x) =
  var y: typeof(x)
  return y

var a = 1
echo test(a)

Fixing the bug and keep typeof(x) is int, not var int seems hard.
When instantiating a generic proc, typeof(x) is already expanded and there is no way to know whether tyVar in return type is a result of typeof(x) or user wrote var int.

[Araq]

typeof can grow another variant KeepTypeModifiers but the defaults must remain the same.

[Araq]

It makes no sense to allow for inconsistent type modifiers for an or-type. The case we should support is this:

proc testOrSink(v: sink (string | seq[int]))

[demotomohiro]

fixed it.