wayland: Make implicit grabs during popups be owner_events=TRUE

Getting crossing events is necessary between client surfaces while there is a popup grab in effect (e.g. allow press-drag-release in menus), we should only stick with the focus surface while the pointer is outside any client surface.

This partially undoes commit 79050004 (or, at least, mutter no longer fixes the bug it claimed to fix). This will be addressed in gtk4.