fix: Improve performance of base64 detection regex

shared/utils/urls.ts

@@ -86,6 +86,17 @@ export function isExternalUrl(url: string) {
   return !!url && !isInternalUrl(url) && !url.startsWith(creatingUrlPrefix);
 }
 
+/**
+ * Returns match if the given string is a base64 encoded url.
+ *
+ * @param url The url to check.
+ * @returns A RegExp match if the url is base64, false otherwise.
+ */
+export function isBase64Url(url: string) {
+  const match = url.match(/^(data:[a-z]+\/[^;]+;base64,(.*))/i);
+  return match ? match : false;
+}
+
 /**
  * For use in the editor, this function will ensure that a url is
  * potentially valid, and filter out unsupported and malicious protocols.