Encode params in URLSearchParams

Summary:
URL params are not encoded which could cause a security risk, for more details pls see https://fb.workplace.com/groups/react.technologies.discussions/permalink/3184249088473474/

Changelog:
[General][Security] - Encode URL params in URLSearchParams.toString()

Reviewed By: yungsters

Differential Revision: D34415119

fbshipit-source-id: 83c29df9427ad0adc9b6a2b4d0ff5494247aa5cb

Libraries/Blob/URL.js

@@ -101,7 +101,13 @@ export class URLSearchParams {
     }
     const last = this._searchParams.length - 1;
     return this._searchParams.reduce((acc, curr, index) => {
-      return acc + curr.join('=') + (index === last ? '' : '&');
+      return (
+        acc +
+        encodeURIComponent(curr[0]) +
+        '=' +
+        encodeURIComponent(curr[1]) +
+        (index === last ? '' : '&')
+      );
     }, '');
   }
 }