[Wayland] mutter - focus out/in is sent to toplevel window when it's dragged and moved

When toplevel window is dragged and moved, it gets focus in/out events. That breaks Firefox appearance on Wayland:

https://bugzilla.mozilla.org/show_bug.cgi?id=1491808

and also causes issues with moving toplevel window under Wayland as it's marked as unfocused.

test-focus.c

There's a simple testcase which demonstrates different behavior of toplevel window on Wayland/Mutter, X11/Mutter and Weston. Run the testcase, drag the toplevel window and move it. X11/Mutter and Weston works fine but Wayland/Mutter is broken.

Weston and X11: $ GDK_BACKEND=x11 ./test-focus ********** Focus in event

Wayland/Mutter: $ ./test-focus ********** Focus in event ********** Focus in event ********** Focus out event ********** Focus in event