meta_wayland_seat_repick() can be called in various cases while mutter
has a GRAB_OP ongoing which means we could be sending wrong pointer
enter/leave events.
https://bugzilla.gnome.org/show_bug.cgi?id=726123
This ensures that we send the proper leave and enter events to wayland
clients.
Particularly, this solves a bug in SSD xwayland windows where clicking
and dragging on the title bar to move the window only works on the odd
turn (unless the pointer moves away from the title bar between
tries). This happens because xwayland gets a button press but doesn't
see the release so when it gets the next button press it discards it
because its pointer button tracking logic says that the button is
already pressed. Sending the proper wayland pointer leave event fixes
it since wayland clients must forget about button state at that point.
https://bugzilla.gnome.org/show_bug.cgi?id=726123
At one point, it was supported to run mutter without a compositor,
but we don't allow that any longer. A lot of code already assumes
display->compositor exists and doesn't check for a NULL pointer,
so just kill the rest of the checks.
This is specifically about managing X11 windows, not necessarily
running as an X11 compositor. By that I mean that this code is
still used for XWayland windows, and event handling is still and
modesetting / monitor management is still in core/.
This is also a fairly conservative move. We don't move anything
like screen.c or bell.c in here, even though those are really
only for X11 clients.
This is fairly simple and basic for now, with just skip_taskbar /
skip_pager, but eventually a lot of "WM policy" like this, including
move-resize, will be in subclasses for each individual surface.
In particular we need to know about all key events to keep the xkb
state reliable even if the event is then consumed by a global shortcut
or grab and never reaches any wayland client.
We also need to keep track of all pressed keys at all times so that we
can send an updated set or pressed keys to the focused client when a
grab ends.
https://bugzilla.gnome.org/show_bug.cgi?id=722847
Any given clutter event carries the modifier state as it was before it
occured but, for the wayland modifiers event, we want the state
including the current event.
To fix this, we'll keep our xkb_state instance around instead of the
serialized mods.
https://bugzilla.gnome.org/show_bug.cgi?id=722847
