Add hover info for custom types

[unknown]

Adds hover info for custom types and closes #4451.

I marked this PR as a draft, because the behavior I implemented differs slightly from the original proposed behavior I proposed. See #4451 (comment) for more context. Otherwise, this is ready to be reviewed.

This PR changes the language server display type info like the following:

//// wibble.gleam

type Wibble {
  // ^ Wibble

  Wibble(Int)
  // ^ Wibble(Int)

  Wobble(label: String)
  // ^ Wobble(label: String)
  //     ^ String
}

[lpil]

Thank you. I've left a note inline

[lpil]

This is different from the format we use for variants!

Can we reuse the existing code to ensure they are the same?

[unknown]

Yeah I made a note of that here: #4451 (comment)

It's been a while since I worked on this, but if I remember correctly, the reason it differs is because RecordConstructor doesn't store any information about the custom type its a member of (aka the return type of the constructor). Should I add a string in RecordConstructor with the name of the custom type?

Not sure if there are other approaches, but adding a string wouldn't allow for code reuse. The return type would have to be a Type.