We refuse to move focus while a grab operation is in place. While this
generally makes sense, there's no reason why the window that owns the
grab shouldn't be given the regular input focus as well - we pretty
much assume that the grab window is also the focus window anyway.
In fact there's a strong reason for allowing the focus change here:
If the grab window isn't the focus window, it probably has a modal
transient that is focused instead, and a likely reason for the focus
request is that the transient is being unmanaged and we must move
the focus elsewhere.
https://gitlab.gnome.org/GNOME/mutter/issues/15
(cherry picked from commit 148da24f9510ebd23d750b8224aa0ab3a549e69e)
a83e72d7c1