Implement renaming for Functions, Constants and Type Variants

[GearsDatapacks]

This PR closes #3259
This is pretty much ready, except for two things:

• It's missing tests
• There's an annoying bug to do with module shadowing which I still have to figure out how to resolve

[GearsDatapacks]

Ok, this is ready for review now. I'm not super happy with the way I fixed the module access shadowing bug, but I couldn't think of another way to do it. Let me know if you have any thoughts.

[lpil]

Super nice!! I'm really excited about this one.

I've not finished reviewing totally but I've gotta go so I wanted to drop my thoughts so far. See inline notes.

[GearsDatapacks]

Ok, I have now added the reference information to the cache so we can rename values in cached modules.
It feels a bit wasteful, it's quite a lot of information which is only needed for the LSP, but I don't think there's any other way around it.
I have responded to a couple of your comments, let me know your thoughts.

[GearsDatapacks]

This should be ready for review again.
As discussed on Discord, I couldn't find a way to easily represent the information needed for renaming in a call-graph structure. Instead, I've added a ReferenceTracker struct, which keeps track of all the reference locations, but also builds a call graph which can later be used (in a future PR) to do usage tracking.
I have also changed the functionality so that renaming a value that is imported in an unqualified fashion now aliases it instead of globally renaming, and prevented users from renaming values from external packages.