If two cursor buttons are pressed at the same time, the client will now
be notified of the second button press.
The main reason for not sending the concurrent presses was due to an
early return in dispatch_cursor_button if a seatop is in progress. This
patch makes it call seat_pointer_notify_button prior to returning. But
it also has to make sure there's not a mismatch in events such as a
release without a press.
Prior to this patch, the down seatop would send press and release events
in its begin and finish functions. No other seatops did this. A press
event would be sent prior to starting tiling drag, but never an
associated release.
After this patch, no seatops send their own press or release events. We
send them prior to calling the seatop begin functions, then the first
part of dispatch_cursor_button handles all presses during seatops and
when releasing the seatop.
All seat operations except "down" eat the button pressed event and don't send
it to clients. Thus, when ending such seat operations we shouldn't send the
button released event.
This commit moves the logic used to send pressed/released into the "down"
operation.
This splits each seat operation (drag/move tiling/floating etc) into a
separate file and introduces a struct sway_seatop_impl to abstract the
operation.
The move_tiling_threshold operation has been merged into move_tiling.
The main logic for each operation is untouched aside from variable
renames.
The following previously-static functions have been made public:
* node_at_coords
* container_raise_floating
* render_rect
* premultiply_alpha
* scale_box
