wayland: Simplify the move/resize code

The old protocol is out of date and broken for resizing at the
top/left. This is still as broken, but a lot simpler.
window: Use the window's rect for checking whether this is a resize

The expected_rect is going to die.
window: Add proper interpretation of dx/dy

dx/dy should be against the regular window's rect, and need to
be ignored when we're resizing. Instead, we use gravity to anchor
the window's new rectangle when resizing.
wayland: Don't move the window when we're simply sending out a configure

If we're sending out a configure event, we can't immediately move the
window; we need to instead wait to apply the new position when the
client sends a new buffer.
wayland: Move the RESULT_RESIZED code to the proper place

We need to set this when we update window->rect, not when we simply
send out a configure event.