Fix LSP documentSymbol marking every symbol as deprecated

[garrettr]

What

textDocument/documentSymbol responses unconditionally set Tags to [SymbolTagDeprecated] for every symbol. Per the LSP spec, clients prefer tags over the legacy deprecated boolean, so the unconditional tag won and every symbol in every .proto file rendered with a strikethrough in editors that honor symbol tags — in VS Code that's the Outline panel, breadcrumbs, sticky scroll, and Go to Symbol (Cmd+Shift+O).

This change only includes SymbolTagDeprecated in Tags when the symbol is actually deprecated.

It also fixes the deprecation check itself: it previously discarded the value returned by AsBool() and only checked the ok return, so an explicit option deprecated = false; would also be reported as deprecated. Use the returned boolean value directly.

Why

Introduced in #4311, first released in v1.65.0. Reproduction and full details in #4530.

Fixes #4530

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[doriable]

This fix looks good, thank you for catching and submitting this!
A quick comment: would you mind adding a regression test case for this in diagnostic_test.go? As an aside, I'll look into the CVE's, it seems we'll need to upgrade our go version to address that, I can handle that from our end.

(EDIT: a PR has been opened to upgrade the Go version #4532)

[garrettr]

Thanks for the review! Added a regression test in document_symbol_test.go (the existing textDocument/documentSymbol test — there isn't a diagnostic_test.go and the bug is in the documentSymbol path rather than diagnostics, so I extended the test that was already exercising it).

The existing test already had a deprecated LegacyDocument case but only asserted on the legacy Deprecated boolean, not Tags, which is why it didn't catch this. The test now asserts Tags for every symbol, and I added an ExplicitlyNotDeprecated message with option deprecated = false; to pin down both the unset and explicitly-false cases.

Verified the new assertions fail against the pre-fix symbol.go ("symbol X has wrong tags" for every non-deprecated symbol) and pass with the fix.

[garrettr]

I'm still waiting for my employer to approve the CLA. I will sign it (or close the PR without signing) when I hear back from them.