wayland: Fix windows shrinking when output layout changes

When the output layout changes, the Workspace is going to update the
struts and then go through every window and see whether it should be
moved or resized.

On the other hand, the layer shell windows react to output changes on
a timer. Furthermore, it's not synchronized with the workspace rearranging
the managed windows. It means that when Workspace::desktopResized() runs,
the panel struts can be slightly outdated, i.e.

- An output layout change occurs
- Workspace::desktopResized() is called but the struts can be wrong
- some time later, LayerShellV1Integration::rearrange is called, it
  fixes layer shell window geometries and struts
- after the layer shell integration has finished rearranging the
  layer shell windows, it calls Workspace::desktopResized(), but the
  damage had already been caused

With the proposed change, the Workspace and the LayerShellV1Integration
will rearrange the windows in sync.

CCBUG: 482361
(cherry picked from commit a489bfa1)