[3.x] Mark node groups as dirty for every children if parent is moved

[YuriSizov]

Backport of #61577.

As much as I wish it for 3.5, it's probably too risky. But maybe 3.5.1?

[lawnjelly]

Agree with @reduz that this has the potential to be overly expensive, especially if there are any calling points that call move_child() in a loop, where this propagation might happen multiple times.

This is similar-ish in concept to the problems in #61929 .

Agree this is probably best merged after 3.5 stable so we can test for performance regressions.

[YuriSizov]

Yeah, that's my concern overall, but I think it shouldn't be too bad. This only marks the groups for an update, but update itself happens on the next frame, once per group, I believe. So the number of nodes should not contribute as much as variety of groups. We can also limit what groups we want to update (only processing order related ones?) and mark them always, without propagating.

[YuriSizov]

Should be safe to merge now, I guess. Whether or not to push it to 3.5.x, I don't know.

[akien-mga]

Thanks!

[akien-mga]

I suggest erring on the side of caution and not cherry-picking this for 3.5.1 (as we'd likely get less testing for 3.5.1 RC 1 as we got for 3.5 RCs and thus little chance to actually spot potential issues in this core code). It does look fairly safe so if it's really needed I'm happy to reconsider but I think our time is better spent making sure that 3.6 gets released fast :)