Rebase cursor on layer rearrange

[cedws]

Closes #3080.

I'm not sure if this is the correct way of doing it.

[emersion]

Maybe we should just commit a transaction in this case?

@RyanDwyer Thoughts?

[RyanDwyer]

While this works, it can be wasteful because there's probably other code somewhere that arranges layers and calls cursor_rebase itself. This commit would cause it to be rebased twice in this case.

I'd prefer it to be rebased from handle_layer_shell_surface.

[emersion]

What if a layer surface is resized? We need to rebase in this case too.

(I think we want to detect when we need to re-arrange layers, instead of doing it at every single commit.)

[cedws]

Could you distil what I need to do? I can move the cursor_rebase code into handle_layer_shell_surface, but if you're asking me to detect when we need to re-arrange layers, I don't know how that would be done.

[emersion]

detect when we need to re-arrange layers

Right now we re-arrange layer surfaces at each commit, even if they still keep the same size. This is unnecessary.

For this PR we could probably just rebase the cursor in handle_layer_shell_surface, which is necessary anyway. Not re-arranging when a layer surface doesn't resize is a follow-up issue.

[cedws]

I tried moving it into handle_layer_shell_surface, but that doesn't seem to fix the case I'm testing swaywm/swaylock#32 (comment).

[emersion]

Superseded by #3665