Add minimum polyfill to support "relative-time-element" in PaleMoon (#26575) (#26578)

Backport #26575 by @wxiaoguang

Close #26525

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
(cherry picked from commit 1f29cfa683)

web_src/js/webcomponents/polyfill.js

@@ -0,0 +1,17 @@
+try {
+  // some browsers like PaleMoon don't have full support for Intl.NumberFormat, so do the minimum polyfill to support "relative-time-element"
+  // https://repo.palemoon.org/MoonchildProductions/UXP/issues/2289
+  new Intl.NumberFormat('en', {style: 'unit', unit: 'minute'}).format(1);
+} catch {
+  const intlNumberFormat = Intl.NumberFormat;
+  Intl.NumberFormat = function(locales, options) {
+    if (options.style === 'unit') {
+      return {
+        format(value) {
+          return ` ${value} ${options.unit}`;
+        }
+      };
+    }
+    return intlNumberFormat(locales, options);
+  };
+}

web_src/js/webcomponents/webcomponents.js

@@ -1,3 +1,5 @@
 import '@webcomponents/custom-elements'; // polyfill for some browsers like Pale Moon
+import './polyfill.js';
+
 import '@github/relative-time-element';
 import './GiteaOriginUrl.js';