Merge commit '3f6887557b23d363e7f8f18518db4447739d64bb' into glitch-soc/merge-upstream

Conflicts:
- `app/javascript/entrypoints/common.js`:
  Upstream moved everything from `app/javascript/packs` to
  `app/javascript/entrypoints` while this file was a glitch-soc
  addition. Moved it like the rest.
- `tsconfig.json`:
  Conflict due to glitch-soc's flavor.
  Updated like upstream.

Also moved and updated the following files accordingly:
- `app/javascript/flavours/vanilla/theme.yml`
- `app/javascript/flavours/glitch/theme.yml`
- everything in `app/javascript/flavours/glitch/packs`

app/javascript/flavours/glitch/entrypoints/application.js

@@ -0,0 +1,15 @@
+import '@/entrypoints/public-path';
+
+import { start } from 'flavours/glitch/common';
+import { loadLocale } from 'flavours/glitch/locales';
+import main from "flavours/glitch/main";
+import { loadPolyfills } from 'flavours/glitch/polyfills';
+
+start();
+
+loadPolyfills()
+  .then(loadLocale)
+  .then(main)
+  .catch(e => {
+    console.error(e);
+  });