core: Remove a few unused meta_core functions
window: Fix typo in comment
window: Simplify adjust_for_gravity
window: Remove the borders parameter from adjust_for_gravity

We can simply use the existing cached borders.
window: Move the session restoration and post-manage move_resize to window-x11
window: Move adjust_for_gravity to window-x11

This removes the weirdness about which edge cases are where in the
move_resize_internal API, and we now always pass in client top-left
coordinates.
window: Make the x/y position in the requested_rect more accurate

For gravity-based resizing, we need to make sure that the requested
rectangle has the proper x/y position given by the gravity resize,
rather than the bogus root_x_nw / root_y_nw parameter.

Make the test for this more explicit.
window: Remove some ugly debug logging