tiling: Evacuate tiled windows from custom & quick tiling on output removal
Context: If a display is removed, the corresponding TileManager is removed with it. This in turn removes every one of its Tiles with it, and when a Tile's destructor is called, it attempts to find a new replacement tile for any windows it was previously managing.
However, if the Tile is removed because its corresponding TileManager has been removed, this has the potential to cause a segfault in KWin, causing it to crash (I suspect a possible race condition? but not sure).
This MR correctly evacuates custom tiled windows & migrates quick tiled windows upon output removal.
(cherry picked from commit 0ca7b40d)