xwayland: Change layer for xwayland override redirect windows

Our positioning of override redirect windows falls apart when an app is on the fullscreen layer, because we end up putting its menus and tooltips beneath it. This patch raises the special override redirect layer to be just below things like on-screen keyboards (and, unfortunately, above things like panels).

There is no perfect way to deal with this problem, especially for content like tooltips that don't come with transience hints.

In some cases override redirect menus could be better placed by using the parenting/transience information provided with them at map time, and we should probably do that at some point, but that would still leave us with tooltips below full screen applications, and the need for this layer change.

based on a patch Co-authored-by: Hideyuki Nagase hideyukn@microsoft.com Co-authored-by: Steve Pronovost spronovo@microsoft.com Co-authored-by: Brenton DeGeer brdegeer@microsoft.com

I changed the layer position and the comments, so: Signed-off-by: Derek Foreman derek.foreman@collabora.com