Implement renaming for local variables

[GearsDatapacks]

Closes #2956
This PR implements renaming of local variables in the Language Server including:

• Setting up the new route and server capability
• Setting up a test environment for testing renaming
• Tree walking to find references to the variable
• Rejecting renames if an invalid name is provided (e.g. renaming a variable to SomeVar)

A few things I did while implementing this:

• I used definition location to decide whether two variables were the same. That's mainly because since variable shadowing exists in Gleam, two variables with the same name don't necessarily refer to the same variable.
• To allow renaming to also rename references to variables in clause guards, I added a definition_location field to the ClauseGuard::Var variant. Since ClauseGuard is just one type for both typed and untyped versions, this field has to be present in the untyped AST, where it has no meaning (we don't know where the variable is defined yet). That was the most straightforward solution I could find for the time being.
• Similarly, I added clause guards to the AST visitor. I only really implemented the bare-bones for what this PR needs; it seemed a bit wasteful to implement it all. I'll probably open a separate PR to implement the full visitor for it

[GearsDatapacks]

Not sure why checks are failing... I haven't changed anything to do with deps or cargo deny

[lpil]

Ahhh this is so exciting!! Amazing! I've left one question inline

[GearsDatapacks]

I have now made it work properly with:

• Assignment patterns (e.g. 1 as one)
• Label shorthand
• Arguments

One thing I wasn't totally sure about is the following:

let Wibble(wibble:) = todo
//         ^ If you put you cursor here and trigger a rename

What should happen? Should it treat is as renaming the local variable: wibble: wobble, or should it (once we have this feature implemented) rename the label itself? The latter is probably something we want eventually, however currently this PR implements the former. Let me know what you think

[GearsDatapacks]

Just realised that the prepare_rename function wasn't up-to-date with the regular rename function. I've now fixed that and checked prepare_rename in the tests, so that shouldn't happen in the future. However, it is quite a lot code duplication. All the pattern matching has to be performed in two different places. I wonder if there's a way around this

[lpil]

Fantastic!!! I love this!

I found a tiny bug, it's not renaming variables used in bit array literals

pub fn starts_with(bits: BitArray, prefix: BitArray) -> Bool {
  let prefix_size = bit_size(prefix)

  case bits {
    <<pref:bits-size(prefix_size), _:bits>> if pref == prefix -> True
    _ -> False
  }
}

Try renaming prefix_size here

[GearsDatapacks]

Yay, another edge-case. I'll look into it