Add completion detail

[PgBiel]

Draft as I couldn't get it to work with Zed for some reason, right now only VSCode is working. Will investigate.

(EDIT: Turns out this will require a PR to c3-zed to work with Zed. That means it isn't the LSP's fault, so the PR itself should be fine. However, I'll keep it as a draft as I'll need to rebase on #103 later. (Done!))

Basically, this adds type information as well as other information to completions, making them more immediately helpful.

This was inspired by a similar feature in the Gleam language's LSP.

I chose to simply add a "Type" hint for struct, bitstruct and union as I felt like being more specific wouldn't be too helpful, but let me know if you'd prefer to have "Struct", "Bitstruct" and "Union" instead (I'd be ok with that as well, the former just felt a bit cleaner to me, but I don't mind it that much).

I also chose "Enumerator" for enum values, but I'm thinking of writing just "Enum value" as that's clearer. (Changed to "Enum Value")

Also, I chose "Fault Constant" for fault constants and "Struct member 'name'" for anonymous substructs.

In addition, defs display "Type" when they're type aliases, or "Alias for ''" otherwise since we have little to no semantic information (as an exception, I also display "Alias for macro '@macroname'" when we know for sure it's a macro due to @).

Future work

• Perhaps some way to resolve the definition RHS to display better information would be nice.

Screenshots

[pherrymason]

Thank you again!