Fix CJK fonts again and misc. font issues (#14575)

* Push system-ui further down the stack, fix #12966

* Fix Firefox showing U+300x in emoji font and more

* Revert emoji font and fix long-standing Safari bug

* Exclude Safari emoji fix above 1.25x zoom

* Minor correctness/typo fix, affects only legacy platforms

* Emoji consistency for monospace (e.g. EasyMDE)

* Override paradigm; macOS/iOS-specific metric fix

* Move whitespace fix to font-face

* Handle metric calculation errors with Firefox

* One last workaround for aliased fonts in Linux

web_src/js/index.js

@@ -26,7 +26,7 @@ import {initNotificationsTable, initNotificationCount} from './features/notifica
 import {initStopwatch} from './features/stopwatch.js';
 import {createCodeEditor, createMonaco} from './features/codeeditor.js';
 import {svg, svgs} from './svg.js';
-import {stripTags} from './utils.js';
+import {stripTags, mqBinarySearch} from './utils.js';
 
 const {AppSubUrl, StaticUrlPrefix, csrf} = window.config;
 
@@ -2519,6 +2519,19 @@ $(document).ready(async () => {
       .attr('title', '');
   });
 
+  // Undo Safari emoji glitch fix at high enough zoom levels
+  if (navigator.userAgent.match('Safari')) {
+    $(window).resize(() => {
+      const px = mqBinarySearch('width', 0, 4096, 1, 'px');
+      const em = mqBinarySearch('width', 0, 1024, 0.01, 'em');
+      if (em * 16 * 1.25 - px <= -1) {
+        $('body').addClass('safari-above125');
+      } else {
+        $('body').removeClass('safari-above125');
+      }
+    });
+  }
+
   // Semantic UI modules.
   $('.dropdown:not(.custom)').dropdown({
     fullTextSearch: 'exact'