This improves LSP handling of `map` types, including completions for the
keyword and types within `<` angle brackets `>`. It also fixes up
semantic tokens to properly tokenize maps, and removes document
highlighting from map types (which aren't meant to be reference-able),
and adds hover documentation for maps.

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

#4309)

These are unenforceable, because `repeated` and `map` fields do not
track field presence.

Ref: https://protovalidate.com/schemas/standard-rules/#field-presence

Fixes #3812.

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Also removes the diagnostic.Data from the new diagnostics, which AFAICS
is unused; we can save ourselves the json marshaling.

As a part of this, added a first pass at adding tests for diagnostics;
we don't currently have any. These are a bit different because we
haven't implemented [PullDiagnostics][1] (we can add this, but we'd need
a custom implementation, or wait until [go.lsp.dev upgrades to
3.17][2]). Instead, we intercept the notifications from the
server. Lastly, since we don't actually want the tests to wait around,
adds synctest and only runs the tests on Go 1.25 for now (1.26 should be
released next month and we'll be able to upgrade to 1.25 as our
minimum).

This is in preparation to eventually landing relatedInformation (other
spans) in diagnostics, from bufbuild/protocompile#659.

Also pulls in the latest protocompile@main to bring in the new
deprecated tag.

[1]: https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_pullDiagnostics
[2]: go-language-server/protocol#52