Rework script external modification tracking

[KoBeWi]

Fixes #101579

I introduced a new struct EditedFileData in ScriptEditorBase, which holds basic data about the edited file - path and modified time. The path is used instead of the previous _edit_res_path meta, the modified time is used instead of Resource's "modified time", which is not file modified time.

Due to #101615 the changes can't be properly tested.

[YeldhamDev]

I can still trigger the bug even with this PR (Fedora - GNU/Linux).

Nevermind, used the wrong executable. This fixes it on my end.

[Repiteo]

Thanks!

[Jordyfel]

@KoBeWi I am investigating uses of Resource.set_path_cache() in order to improve its documentation, since it got exposed recently.

What was the reason for this use in filesystem dock? The resource paths are updated right after this in _update_resource_paths_after_move, so this doesn't get in front of anything. In fact it would sabotage that logic, because the function would find the resource paths at the new path and decide that they don't need a set_path() call which would normally move them in the resource cache.

I tested and, on master, trying to move a script of an open scene generates an error on the second move, which is fixed after commenting out this call.

Worth noting that the recent revert of the gdscript set_path_cache() override would have changed this behavior

[KoBeWi]

tbh this looks like some previous solution I tried and forgot to remove. I can't remember why this change exists.