core/placement: change quicktile hotkeys to work relatively

Currently, the quicktile hotkeys are "absolute" in the sense that pressing "Meta+Left" always tile the window to the left half of the screen, regardless of its current quicktile position.

!50 (merged) @ngraham partially changed this behavior so that if you press "Meta+Left" followed by "Meta+Up" in one second, the window will be tiled to the top-left.

This commit generalizes the above behavior so it works any time, without the one-second limit. This is inspired by the COSMIC desktop's design.

demo: Screencast_20240901_072013

The new behavior is as follows:

+--------------+-------------+--------------+-----------+--------------+
| current pos  |  key:left   |    right     |    up     |     down     |
+--------------+-------------+--------------+-----------+--------------+
| left         | no change   | restore      | top-left  | bottom-left  |
| right        | restore     | no change    | top-right | bottom-right |
| up           | top-left    | top-right    | no change | restore      |
| down         | bottom-left | bottom-right | restore   | no change    |
| top-left     | no change   | top          | no change | left         |
| top-right    | top         | no change    | no change | right        |
| bottom-left  | no change   | bottom       | left      | no change    |
| bottom-right | bottom      | no change    | right     | no change    |
| normal       | left        | right        | top       | bottom       |
| maximized    | left        | right        | top       | bottom       |
+--------------+-------------+--------------+-----------+--------------

Diagonal hotkeys like "quicktile to top-left" are processed as left then up.

Pros:

• I find this model ("moving / spanning window to this direction") more natural.
• Currently when a window is already tiled to left and the user presses "meta+left" again, it moves to the screen on the left side, and tiles to right. This also matches the "moving window" mental model than an absolute one.
• Fewer key presses to move a window to adjacent positions, e.g. from "left" to "top-left".

Cons:

• More key presses to move a window to the opposite position, e.g. it now requires two "meta+right" to move a window from "left" to "right".