This modifies `seat_cmd_cursor` to utilize `get_mouse_button` when
parsing mouse buttons for the `press` and `release` operations. All x11
buttons, button event names, and button event codes are supported.
For x11 axis buttons, `dispatch_cursor_axis` is used instead of
`dispatch_cursor_button`. However the `press`/`release` state is ignored
and the either axis event is processed. This also removes support for
`left` and `right` in favor of `BTN_LEFT` and `BTN_RIGHT`.