General optimizations

[itzexor]

Simple profiling with the GJS/CJS profiler revealed:

1. paths being called relatively frequently when the features they support weren't enabled:
   -magnifier cursor update
   -desklet mouse tracker
2. window restack connections are always a top consumer on general non-cinnamon-ui usage
3. uiGroup is always allocating, and the allocate does nothing beyond default
4. notification daemon is always checking the WindowTracker to clear notifications, even when there are none

[jaszhix]

Just for reference, this was closed after discussions on Slack. I did not intend for this to be closed. There were two problems I pointed out:

• 885582d switches uiGroup to an StWidget actor, but this loses the skip_paint optimization in CinnamonGenericContainer, and seemed less responsive. I tried to benchmark this with gputest, which might at least show the impact Cinnamon has on the GPU.

Since uiGroup is now entering clutter_actor_paint, before it returns early from the opacity override that skip_paint was replaced with, it places a lock on ClutterContext via _clutter_context_get_pick_mode which calls _clutter_context_get_default. I've seen this affect frame times and have consequently reduced clutter_get_default_backend calls in other PRs because of this.

In addition, this has led me to think allocating in JS with GenericContainer is not the bottleneck, especially if what it's doing is less resource intensive than Clutter's base allocation vfunc.

• 2dd1532 slows the cursor movement. I'm not sure why. It seems like a muffin or xorg bug which had less impact while Cinnamon was polling XQueryPointer.

[itzexor]

• rebased on master
• dropped uiGroup commit to another branch for future investigation
• fixed up magnifier commit to cover hopefully all cases where it can be first called.

i think the desklet one definitely wastes resources if you're not using desklets. i'd like to keep that one in if possible.

[itzexor]

• rebased on master
• fixed mistake in magnifier.js where I replaced new Object(roi) with Object.Clone(roi) (non existent function) instead of Object.assign({}, roi) as I meant to. This gets rid of a "use an object literal" warning.

I think this is resolved.