Enable the object-shorthand ESLint rule in src/shared

Please see http://eslint.org/docs/rules/object-shorthand.

For the most part, these changes are of the search-and-replace kind, and the previously enabled `no-undef` rule should complement the tests in helping ensure that no stupid errors crept into to the patch.

src/core/bidi.js

@@ -115,7 +115,7 @@
 
   function createBidiText(str, isLTR, vertical) {
     return {
-      str: str,
+      str,
       dir: (vertical ? 'ttb' : (isLTR ? 'ltr' : 'rtl'))
     };
   }