I18N: Add Lingui core translation framework. (#41827)

* I18N: Add Core Lingui framework for translating the UI

* Make FieldSet accept ReactNode for the label, so it can be translated

* Translate a phrase in the User profile edit form

* Translate phrase

* run lingui compile before webpack builds

* init i18n more lazily

* i1n:compile in drone lint step

* wip for getting tests to work

* Use mock lingui/macros because its too hard to use the real macros in Jest...

* mock messages for tests

* use specific lingui version

* add comment for test helper

* we actually don't need the i18n setup in tests because we mock out <Trans />

* update package.json

* remove unneded imports

* revert back babel core version

* Create a I18nProvider wrapper

scripts/drone/steps/lib.star

@@ -496,6 +496,7 @@ def lint_frontend_step():
         'commands': [
             'yarn run prettier:check',
             'yarn run lint',
+            'yarn run i18n:compile', # TODO: right place for this?
             'yarn run typecheck',
         ],
     }