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.