screenshooter: Choose output to record from based on keyboard focus

Record from the output of the surface that has keyboard focus for the
seat used to activate the recorder key binding. If there is no focused
surface, record from the first one.

Also, use the weston_transformed_region() to transform the damage
region of the output into the coordinates expected by read_pixels().

https://bugs.freedesktop.org/show_bug.cgi?id=71401
1 file changed