LSP add goto definition on parent names

[emcfarlane]

This PR adds support for goto definition based on the cursor position in the fields FullName. For example: google.protobuf.Timestamp can go to both the type Timestamp or the package google.protobuf within the file google/protobuf/timestamp.proto. We may wish to extend this behaviour to also cover going to every file within the package google.protobuf.

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf CI / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Oct 30, 2025, 2:35 PM

[stefanvanburen]

two things, and one weird thing I noticed:

• I think hover should have the same logic as "go-to definition"; that is, if I'm hovering on a symbol and get docs, I would expect go-to definition to bring me to the location where that doc comment comes from. (I think we should add this logic to hover.)
• The UX feels a little weird on the parent types, given the option (buf.validate.field).string.max_len, using go-to-definition:
  • max_len does sorta what I expect (it brings me to BytesRules.max_len; it should bring me to StringRules.max_len 😅)
  • string does sorta what I expect (it brings me to BytesRules, which also defines a max_len, but should bring me to StringRules)
  • field takes me to the package buf.validate line in validate.proto;
• (likewise with google.protobuf.Timestamp, I'm not sure if it's better UX that google doesn't do anything and protobuf just brings me to a file, rather than have the whole thing go to Timestamp?)

[emcfarlane]

Closing in favour of breaking the symbols up, cc @doriable