Merge commit 'c6684aa1e392f2dd86af4362b4259809549abaad' into glitch-soc/merge-upstream

Conflicts:
- `app/views/layouts/application.html.haml`:
  Upstream changed how the `inert.css` file is included.
  The conflict is caused by glitch-soc's theming system.
  Ported the upstream change.

Additional changes:
- `config/webpack/shared.js`: bypass glitch-soc's theming
  system for `inert` pack.

app/javascript/packs/inert.js

@@ -0,0 +1,4 @@
+/* Placeholder file to have `inert.scss` compiled by Webpack
+   This is used by the `wicg-inert` polyfill */
+
+import '../styles/inert.scss';