feat: add displayLang test (#5495)

* feat(e2e): add language extension to setup

This adds a slimmed-down version of the Spanish Language Pack and also
adds a `languagepacks.json` to the e2e `workspaceDir` which allows use
to run a test suite passing the `--locale es` flags to simulate a
different display language.

* feat: add e2e test for display language patch

This tests loading code-server in Spanish using the `--locale` flag.

* fixup!: use JSON.stringify for readability

* fixup!: add comment about langaugepacks temp fix

* fixup!: slim down translations

* fixup!: slim down package.json for lang. ext