Add doc-aliases to functions that have their name changed from godot

[lilizoey]

Several functions have had their function-names changed from godot's name, usually to better match idiomatic rust naming conventions. Such as renaming various get_x() functions to just x(). In addition, we sometimes remove functions in favor of other functions that have identical functionality.

To aid users with finding these functions they should have a #[doc(alias)] referencing the original function name/the function that was removed in favor of it.

In addition we should update Contributing.md to state this as well.

[Bromeon]

Yep, I was recommending this in individual reviews, but it's great to have a focused effort, and document it in the guidelines! 👍

[Bromeon]

How do we want to approach this concretely? This is somewhat open-ended, unless someone volunteers to invest the effort to go through all APIs and check all the renames...

Otherwise I'd like to have issues that have a clear actionable, so that they can be closed at some point and don't clutter the tracker for eternity. This could also be done as an incremental effort, I think 🙂

[Bromeon]

Closing, as I think resources are better spent on adding this incrementally. For example, there have been several doc-alias improvements in recent builtin additions, and I added them for enumerators.