Fix unused identifier diags, LSP tag diags

[jakebailey]

Fixes #2001 (mostly)

Issues:

• The checker's ported code was for the non-suggestion side of things, meaning it entirely skipped these diags when the noUnusedLocals/noUnusedParameters was off, so the grayed out suggestion errors were never even calculated.
• reportUnused didn't actually use suggestionDiagnostics at all, nor have the bit that sets the category to Suggestion on the fly; I re-ported that code.
• The LSP code for checking client capabilities for diagnostics was "correct", except apparently the VS Code LSP client does not send the full set of capabilities for both push and pull diagnostics (specifically, tag support). Pull the info from publishDiagnostics as a backup, which is a hack but works around the problem until we can get v10 of the LSP client.

  "publishDiagnostics": {
      "relatedInformation": true,
      "versionSupport": false,
      "tagSupport": {
          "valueSet": [
              1,
              2
          ]
      },
      "codeDescriptionSupport": true,
      "dataSupport": true
  },
  "diagnostic": {
      "dynamicRegistration": true,
      "relatedDocumentSupport": false
  }
  

The warning vs error thing is actually a VS Code setting, something we will have to do once those are passed in and handled.

[Copilot]

Pull Request Overview

This PR changes how unused identifier diagnostics are handled based on compiler options. Previously, unused variables were only reported as errors when noUnusedLocals or noUnusedParameters flags were enabled. Now, unused identifiers are always checked and reported either as errors (when the respective flag is enabled) or as suggestions (when disabled).

Key changes:

• Unused identifiers are now always checked regardless of compiler options
• When noUnusedLocals/noUnusedParameters are disabled, diagnostics are reported as suggestions instead of being omitted
• Client capability checks for diagnostic tags have been removed from the language server, as the LSP spec requires clients to handle unknown tags

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
internal/checker/checker.go	Refactored unused identifier checking to always run and conditionally report as error or suggestion based on compiler options
internal/ls/diagnostics.go	Removed client capability checks for diagnostic tags and added documentation comment; removed unused slices import

[sheetalkamat]

are there any tests. i dont see any change in tests

[jakebailey]

Unfortunately not, the current fourslash runner does not do diagnostics yet and that's a bigger ask I can tackle separately. I have tested this in the editor, however.

[jakebailey]

Okay, this is now a pure port and should work fine.