`MinimalWindowManager` should reposition windows to an active output when their output is removed

Problem

If a window is on an output that no longer exists, it will remain at a position on that output, even though that is invalid. This applies to all windows except attached (e.g. layer shell, maximized, fullscreen, etc.)

Solution

1. When an output is removed, the MinimalWindowManager should find all windows on that output
2. Those windows should be placed in the next active output
3. Write a MinimalWindowManagerTest for the new functionality