Ignore alt-key hotkeys in text fields (#14942)

Fixes #14862

This used to be the case until #13987, which introduced a hotkey to toggle
the Content Warning field.

Unfortunately, MacOS relies on the “alt” key for many things, including
composing text (see #14862), therefore, even if that makes the CW toggle
hotkey significantly less useful, it makes sense to not interfere with
composing toots.

app/javascript/mastodon/features/ui/index.js

@@ -379,7 +379,7 @@ class UI extends React.PureComponent {
 
   componentDidMount () {
     this.hotkeys.__mousetrap__.stopCallback = (e, element) => {
-      return ['TEXTAREA', 'SELECT', 'INPUT'].includes(element.tagName) && !e.altKey;
+      return ['TEXTAREA', 'SELECT', 'INPUT'].includes(element.tagName);
     };
   }