refactor(sandbox): Include sandbox_worker.js in desktop packaging

Include sandbox_worker.js from the LSP's out/ directory when packaging the extension. The glob in copyLanguageServerAssets didn't match it, so the file shipped in the LSP npm tarball but not in the VSIX. The LSP resolves the worker as a sibling of its main bundle at runtime — without it, sandbox silently breaks when duo.sandbox.enabled is true.

No-op until the installed LSP is bumped past !3218, which is when sandbox_worker.js starts appearing in out/.

Closes https://gitlab.com/gitlab-org/editor-extensions/gitlab-lsp/-/work_items/2238