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.

Built from https://develop.svn.wordpress.org/trunk@41351


git-svn-id: http://core.svn.wordpress.org/trunk@41184 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/js/wp-pointer.js

@@ -6,7 +6,10 @@
 	var identifier = 0,
 		zindex = 9999;
 
-	$.widget('wp.pointer', {
+	/**
+	 * @class $.widget.wp.pointer
+	 */
+	$.widget('wp.pointer',/** @lends $.widget.wp.pointer.prototype */{
 		options: {
 			pointerClass: 'wp-pointer',
 			pointerWidth: 320,