constraints: Don't apply titlebar constraint on non-drag user-op move

2d8fa26c ("core: Pass "frame action" grab operations as an
"unconstrained" grab op") changed the behaviour to treat non-grab
related window moving that has the "user action" flag set to still apply
the "constrain_titlebar_visible" constraint.

The fact that it wasn't applied before was relied upon by some
extensions. While it should arguably exist a better API that for such
extensions to use that have a bit more predictable behavior, until that
is so, restore the old semantics.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2891>