Docs: JSDoc improvements for namespaces.

Improve JS parsing of our inline JSDocs by introducing `@namespace`, `@lends` and `@memberOf`. Helps set the way for showing our JavaScript documentation on developer.wordpress.org, see https://meta.trac.wordpress.org/ticket/3063.

* Define all used namespaces using @namespace.
* Correctly specify in which namespace each class is using @memberOf.
* Define each usage of the extend function as a prototype assignment using @lends.
* Some comment blocks were moved to correct the parsing of certain definitions. 

Props herregroen, atimmer, netweb, SergeyBiryukov.  
Fixes #41682.


git-svn-id: https://develop.svn.wordpress.org/trunk@41351 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/js/shortcode.js

@@ -1,6 +1,10 @@
 // Utility functions for parsing and handling shortcodes in JavaScript.
 
-// Ensure the global `wp` object exists.
+/**
+ * Ensure the global `wp` object exists.
+ *
+ * @namespace wp
+ */
 window.wp = window.wp || {};
 
 (function(){