Improve documentation of some Resource methods

[Jordyfel]

#90969 exposed some methods in Resource, but most of them are only useful for implementing resource formats and are major footguns otherwise. This aims to explain more clearly what they do. Also syncs the already existing comments with these changes.

[RandomShaper]

It may be good to add somethiing like, "See also [method _reset_state]".

I still don't quite get why we need both. @dsnopek, couldn't just reset_state be overridable in GDExtension?

[RandomShaper]

Looks good overall.

[Jordyfel]

Asking for review on this, since it received a thumbs up from a core team member. The discussion on whether the method should stay exposed doesn't apply anymore after 4.4 release.

[Mickeon]

The discussion on whether the method should stay exposed doesn't apply anymore after 4.4 release.

There's still merit to it, actually. I genuinely think the move to expose reset_state was excessive. In all of my efforts to remove setup_local_to_scene, the argument against it is the same. It should probably be deprecated.

But that's beyond the improvements done in this PR.

[Mickeon]

Genuinely a massive improvement. Although, what a mess in the API, with those newly introduced methods. Only their virtual equivalent should've been exposed, probably.

[akien-mga]

Thanks!