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 It means that when Workspace::desktopResized() runs, the panel struts can be slightly outdated, i.e.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.
We need to re-arrange layer shell surfaces, compute new struts and adjust the windows in a single step.
Workspace::updateClientArea() is the best candidate for that, so this change repurposes that function from computing work areas to a generic relayouting function.