Use Hashset for dependency list when moving

[Jordyfel]

Change the save_scene_list() function in EditorNode to take a HashSet for a faster has() call on potentially large lists. Sometimes only one scene needs to be saved, so added a new function to do that without having to create a data structure.

The _find_file_owners() function is executed every time on move or rename, scans the entire filesystem, and pushes paths of files which depend on moved or renamed files into a list.

It seems to me that the list of depending files is a good candidate for a HashSet, since it's a (potentially large) String list which is only iterated over and is likely to get unneeded duplicates.

Also change the other parameter to HashSet, since I changed it to a Vector in #81657 which is a mistake.

[AThousandShips]

Now HashSet (which was introduced into the codebase relatively recently, probably explaining why it was a HashMap before) seems like the perfect data structure for this, since this String list is only iterated over and wants to ignore duplicates.

Doubtful that this was missed, as the person who introduced the HashSet type did the remapping from Map to HashMap

[Jordyfel]

Updated description to the current state of the PR

[KoBeWi]

Not sure why is this labelled as bug. Does it fix anything? Looks like performance enhancement.

[AThousandShips]

Seemed like a bug from the original description, and was due to a mistake in previous update by OP, so it fixes reduced performance caused by a previous PR

[KoBeWi]

The reduced performance only takes effect when renaming or moving files and pretty sure it's only noticeable in very extreme cases.

[AThousandShips]

I'm not sure what to call an introduced performance drop though, feel free to assign a label you feel more appropriate :)

[Calinou]

Could you benchmark this and provide before-after results for comparison? (Ideally, upload a reproduction project as well if size permits it.)

[Jordyfel]

Some limited testing in a copy of my largest (not very large still) project showed no statistically meaningful difference.
If necessary to justify the change, I will try to make a more comprehensive test case or try on a large public project when time allows.

[akien-mga]

Thanks!