Merge commit '284b46fee7ad682b52c99d0455a1134e1d4e3fc3' into glitch-soc/merge-upstream

Conflicts:
- `app/helpers/theme_helper.rb`:
  Upstream added an experimental feature flag to try out theme refactors.
  Glitch-soc's theming system is too different, so skips the new feature flag.
- `stylelint.config.js`:
  Ditto.

stylelint.config.js

@@ -2,6 +2,7 @@ module.exports = {
   extends: ['stylelint-config-standard-scss', 'stylelint-config-prettier-scss'],
   ignoreFiles: [
     'app/javascript/styles/mastodon/reset.scss',
+    'app/javascript/styles_new/mastodon/reset.scss',
     'app/javascript/flavours/glitch/styles/reset.scss',
     'app/javascript/styles/win95.scss',
     'coverage/**/*',
@@ -33,7 +34,7 @@ module.exports = {
   },
   overrides: [
     {
-      'files': ['app/javascript/styles/entrypoints/mailer.scss'],
+      'files': ['app/javascript/styles/entrypoints/mailer.scss', 'app/javascript/styles_new/entrypoints/mailer.scss'],
       rules: {
         'property-no-unknown': [
           true,