Add types for CryptoJS functionality used by web’s crypto.js

Preparation for converting platforms’ crypto.js files to TypeScript
(#1252).

We’ll be removing these types shortly, though, when we stop using the
CryptoJS library in #1239.

src/common/types/crypto-js.d.ts

@@ -1,3 +1,9 @@
+declare module 'crypto-js/build' {
+  import CryptoJS from 'crypto-js';
+  import algo = CryptoJS.algo;
+  export { algo };
+}
+
 declare module 'crypto-js/build/enc-base64' {
   import CryptoJS from 'crypto-js';
   export const parse: typeof CryptoJS.enc.Base64.parse;