chore: Add extension host test GitHub Action annotations

[X-Guardian]

Summary

• On GitHub Actions, extension-host test failures are now reported as error annotations on the TypeScript line that failed, and a pass/fail count is added to the job summary.
• The test runner uses Mocha's built-in github-actions reporter when GITHUB_ACTIONS is set. That is the spec reporter plus the annotations and job summary, and it needs no new dependency. Elsewhere it keeps the spec reporter.
• The reporter places an annotation from the failure's stack. The extension host formats stacks itself and ignores source maps, so the stack names the compiled files in out-test, which are not in the repository. The runner now rewrites those frames to their tests/extension-host/**/*.ts lines through the .js.map files, using Node's module.SourceMap, before the reporter reads them. Failure stacks in the spec output name the .ts lines too, locally as well as in CI.
• No workflow change is needed: Actions sets GITHUB_ACTIONS and GITHUB_STEP_SUMMARY, and both reach the extension host through npm run test:extension-host.

Change Type

• feat
• fix
• refactor
• docs
• test
• chore

Context

User-facing impact

• None. Only the test runner changes.

GitLab scope

• gitlab.com
• self-managed GitLab
• both

Affected areas

• Component Browser
• Hover provider
• Completion provider
• Validation provider
• Cache and refresh behavior
• GitLab API calls/auth/token storage
• Docs only

Validation

Local checks

• npm run compile
• npm test or targeted tests
• Manual verification in VS Code Extension Host

Manual test notes

• Added a temporary test asserting 1 === 2 and ran npm run test:extension-host with GITHUB_ACTIONS=true and GITHUB_STEP_SUMMARY set. All 22 real tests passed. The reporter printed ::error file=tests/extension-host/suite/zzAnnotation.test.ts,line=5,col=12::Expected values to be strictly equal…, which is the assertion's line, and wrote 22 passing and 1 failing to the summary file.
• Without GITHUB_ACTIONS, the output is the spec reporter's with no ::error lines, and the failure's stack names zzAnnotation.test.ts:5:12.
• The temporary test was removed.

Breaking Changes

• No breaking changes
• Breaking changes (describe below)

Risk and Rollback

• Main risks: low. If a frame has no source mapping, it is left as it is, and the annotation falls back to the compiled file.
• Rollback strategy: revert the commit.

Release Notes Draft

• None (test tooling only).

Checklist

• Branch is up to date with target branch
• Commit messages follow conventional commits
• Added/updated docs for behavior or settings changes
• Added/updated tests for new behavior
• No secrets or tokens in code, logs, screenshots, or test fixtures