Add String.replaceAll polyfill

See #6047

doc/changelog.asciidoc

@@ -230,6 +230,10 @@ Fixed
 - A bug in QtWebEngine 5.15.2 causes "renderer process killed" errors on
   websites like LinkedIn and TradingView. There is now a workaround in qutebrowser
   to prevent this from happening.
+- Nextcloud Calendars started using `String.replaceAll` which was only added to
+  Chromium recently (Chrome 85), so won't work with current QtWebEngine
+  versions. This release includes a workaround (a polyfill as a
+  site-specific-quirk).
 
 v1.14.1 (2020-12-04)
 --------------------

qutebrowser/browser/webengine/webenginetab.py

@@ -1144,6 +1144,13 @@ class _WebEngineScripts(QObject):
                 QWebEngineScript.DocumentReady,
                 QWebEngineScript.ApplicationWorld,
             ),
+            # FIXME not needed with 5.15.3 most likely, but how do we check for
+            # that?
+            (
+                'string_replaceall',
+                QWebEngineScript.DocumentCreation,
+                QWebEngineScript.MainWorld,
+            ),
         ]
         if not qtutils.version_check('5.13'):
             quirks.append(('globalthis',

qutebrowser/javascript/quirks/string_replaceall.user.js

@@ -0,0 +1,23 @@
+// Based on: https://vanillajstoolkit.com/polyfills/stringreplaceall/
+/* eslint-disable no-extend-native */
+
+/**
+ * String.prototype.replaceAll() polyfill
+ * https://gomakethings.com/how-to-replace-a-section-of-a-string-with-another-one-with-vanilla-js/
+ * @author Chris Ferdinandi
+ * @license MIT
+ */
+
+"use strict";
+
+if (!String.prototype.replaceAll) {
+    String.prototype.replaceAll = function(str, newStr) {
+        // If a regex pattern
+        if (Object.prototype.toString.call(str).toLowerCase() === "[object regexp]") {
+            return this.replace(str, newStr);
+        }
+
+        // If a string
+        return this.replace(new RegExp(str, "g"), newStr);
+    };
+}