feat: add typescript_tsgo language backend (TypeScript 7 native LSP)

[8SFXIM5]

Summary

Adds typescript_tsgo as a new experimental TypeScript language backend, using tsgo — the native Go-based TypeScript 7 compiler with built-in LSP support.

Closes #1402

Motivation

• No Node.js dependency: tsgo implements the LSP protocol natively in Go, eliminating the need for typescript-language-server + tsserver.js wrapper
• Faster startup: Go binary starts significantly faster than the Node.js-based stack
• Standard LSP: Unlike tsserver's custom protocol, tsgo speaks native LSP via tsgo --lsp --stdio
• Future-proof: TypeScript 7.0 is the direction the TypeScript team is heading

Changes

• New file: src/solidlsp/language_servers/tsgo_language_server.py
  • Uses LanguageServerDependencyProviderSinglePath pattern (recommended approach)
  • Supports ls_path custom setting for user-specified binary path
  • Reuses prefer_non_node_modules_definition from the existing TypeScript backend
• Modified: src/solidlsp/ls_config.py
  • Added TYPESCRIPT_TSGO enum member (marked as experimental)
  • Registered in get_source_fn_matcher() and get_ls_class()
• New file: test/solidlsp/typescript/test_typescript_tsgo.py
  • Tests for symbol discovery, cross-file references, and clean symbol names
  • Reuses the existing TypeScript test repo via _LANGUAGE_REPO_ALIASES
  • Skipped when tsgo is not installed
• Updated: test/conftest.py, pyproject.toml (markers), CHANGELOG.md, docs

Usage

# project.yml
languages: [typescript_tsgo]

Or with custom binary path:

languages: [typescript_tsgo]
ls_specific_settings:
  typescript_tsgo:
    ls_path: /path/to/tsgo

Testing

Tested locally with tsgo 7.0.0-dev.20260421.2 on Ubuntu 22.04. All three core LSP features verified:

• documentSymbol (symbol discovery)
• textDocument/definition (go-to-definition)
• textDocument/references (find references)

Note: CI will skip tsgo tests automatically since tsgo is not yet available as a standard CI dependency. A GitHub Actions step for installing @typescript/native-preview could be added in a follow-up.

[MischaPanch]

I did a shallow review, will re-review again once these comments are addressed and tests for tsgo run through in CI

[MischaPanch]

there's no need for the new test, instead tsgo should be added to the list of languages in the existing typescript tests. The adding can be conditional, but it always should be added in CI, so pls use the in_ci function which we already provide in conftest.

You should modify the pytest workflow to make sure tsgo is available

[MischaPanch]

It should be installed on the fly, like other dependencies that are managed by npm. Pls check how other language servers do that and repeat the pattern here

[MischaPanch]

pls adjust accordingly after addressing the other comments