compositor: add a way to change the keyboard locks

This adds a function weston_keyboard_set_locks() which can be used to
change the state of the num lock and the caps locks, changing the leds too.
Only the evdev and libinput backends supports this, since it doesn't make
sense for embedded sessions.

Tested-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
compositor: add an option to set the default numlock value

Add a new "numlock-on" option in the [keyboard] section of weston.ini
which, if set to true, is used to enable the numlock of the keyboards
attached at startup.

Tested-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
xwm: Check whether the seat is NULL when needed in weston_wm_handle_button

XCB and wayland input event handling exists together in xwm, which can
cause problems. weston_wm_handle_button is called via XCB events, while
it calls weston_wm_pick_seat_for_window, which uses info from compositor
(pure wayland). It is also true in setting and removing flags of frames.
Races can happen in between, when resize of moving flag of the frame is
still set while the button has been released, the picked seat will be
NULL in weston_wm_handle_button, causing crash. We can safely ignore
moving or resizing if this happens. The same applies to c06a180d.

Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=82827
Signed-off-by: Boyan Ding <stu_dby@126.com>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
pixman-renderer: fail to zoom more gracefully

When zoom is activated in the pixman rendered the log is filled with warnings
and all rendering stops.  With this patch the warning is generated once and
rendering continues without zooming.

Closes bug 80258

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=80258
Tested-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>