Merge commit '44cd88adc4e2f4028dcc2b08b98368f0dc90cee4' into glitch-soc/merge-upstream

Conflicts:
- `.github/dependabot.yml`:
  Updated upstream, but we've deleted it.
  Keep it deleted.
- `app/javascript/mastodon/locales/index.js`:
  Reworked upstream, but the code was mostly in
  `app/javascript/locales/index.js` in glitch-soc.
  Updated that file accordingly.
- `app/javascript/packs/public.jsx`:
  Not a real conflict, but different imports in
  glitch-soc and upstream.
- `app/views/layouts/application.html.haml`:
  Conflict due to locales loading and theme system
  discrepancies.
  Updated in our own way.
- `app/views/layouts/embedded.html.haml`:
  Conflict due to locales loading and theme system
  discrepancies.
  Updated in our own way.
- `config/webpack/generateLocalePacks.js`:
  Deleted upstream, as upstream now directly loads the
  JSON at runtime.
  Deleted as well, will switch to runtime loading in
  an upcoming commit.
- `config/webpack/shared.js`:
  Not a real conflict, but different imports in
  glitch-soc and upstream.
- `config/webpack/translationRunner.js`:
  Mostly deleted upstream, to be replaced with `formatjs-formatter.js`
  instead.
  Moved the glitch-soc logic there and deleted the file.

app/javascript/mastodon/load_locale.js

@@ -0,0 +1,14 @@
+import { setLocale } from "./locales";
+
+export async function loadLocale() {
+  const locale = document.querySelector('html').lang || 'en';
+
+  const localeData = await import(
+    /* webpackMode: "lazy" */
+    /* webpackChunkName: "locales/vanilla/[request]" */
+    /* webpackInclude: /\.json$/ */
+    /* webpackPreload: true */
+    `mastodon/locales/${locale}.json`);
+
+  setLocale({ messages: localeData });
+}