Improve UI update_clipping_system comments

[doup]

Objective

• Improve update_clipping_system comments

Solution

• Add extra comments
• Reorder CalculatedClip updating match so it's reads (old, new) vs previous (new, old)
• Remove clone on children iteration

[ickshonpe]

Looks good. No problems with the changes but just got a few (a lot now 😄) suggestions for extra improvements.

[ickshonpe]

I was going to suggest to use set_if_neq but then I checked and we never actually query for changes in CalculatedClip so the neq gate is unnecessary:

Suggested change

	(Some(mut old_clip), Some(clip)) => {
	if old_clip.clip != clip {
	*old_clip = CalculatedClip { clip };
	}
	}
	}
	(Some(mut calculated_clip), Some(inherited_clip)) => *calculated_clip = CalculatedClip { inherited_clip },
	}

[ickshonpe]

#8095 that is very related needs some reviews, be grateful if you have a few minutes spare to look at it.

[doup]

Thanks for the comments! I was going to review them, but suddenly I'm getting a segfault out of nowhere. So frustrating. The good thing is that I can learn how this kind of stuff is debugged.

Anyway, sure I can check #8095. Btw, I want to review more UI PRs (mostly yours and nico's), but first I want to finish reading the UI related code. I did few reviews last couple of weeks but I realized I was lacking understanding. ^_^

[doup]

@ickshonpe I've applied most of the suggestions. I think I'm going to skip #8147 (comment) I prefer not to touch that part. In any case, I've asked about it in https://github.com/bevyengine/bevy/pull/8095/files#r1144342397, we can follow there.