LSP 3.16: Fill in the CodeDescription URI to get more information about a diagnostic

[kjeremy]

LSP 3.16 introduces the CodeDescription type which we can use to fill in a URI that contains additional information about a diagnostic.

For example in the following case:

We could fill the field with "https://doc.rust-lang.org/error-index.html#E0425". This would also be really nice for clippy.

See: https://microsoft.github.io/language-server-protocol/specifications/specification-3-16/#diagnostic

[kjeremy]

@Veykril Since you're in this area...

[Veykril]

Oh that sounds quite nice to have, especially for clippy, I can try giving that a look later 👍