Merge branch 'main' into glitch-soc/merge-upstream

Conflicts:
- `app/javascript/mastodon/locales/ja.json`:
  Upstream change too close to a glitch-soc-specific string.
  The glitch-soc-specific string should not have been in this file, so it
  has been moved to `app/javascript/flavours/glitch/locales/ja.js`.
- `app/javascript/packs/public.js`:
  Upstream refactored a part, that as usual is split and duplicated in various
  pack files. Updated those pack files accordingly.
- `app/views/layouts/application.html.haml`:
  Upstream fixed custom.css path in a different way than we did, went with
  upstream's change.

app/javascript/packs/public.js

@@ -144,8 +144,31 @@ function main() {
     });
   });
 
+  const toggleSidebar = () => {
+    const sidebar = document.querySelector('.sidebar ul');
+    const toggleButton = document.querySelector('.sidebar__toggle__icon');
+
+    if (sidebar.classList.contains('visible')) {
+      document.body.style.overflow = null;
+      toggleButton.setAttribute('aria-expanded', false);
+    } else {
+      document.body.style.overflow = 'hidden';
+      toggleButton.setAttribute('aria-expanded', true);
+    }
+
+    toggleButton.classList.toggle('active');
+    sidebar.classList.toggle('visible');
+  };
+
   delegate(document, '.sidebar__toggle__icon', 'click', () => {
-    document.querySelector('.sidebar ul').classList.toggle('visible');
+    toggleSidebar();
+  });
+
+  delegate(document, '.sidebar__toggle__icon', 'keydown', e => {
+    if (e.key === ' ' || e.key === 'Enter') {
+      e.preventDefault();
+      toggleSidebar();
+    }
   });
 
   // Empty the honeypot fields in JS in case something like an extension