Docs: Improve wp-admin JSDoc structural data globally.

JSDoc takes it structural data from `@namespace`, `@lends` and `@memberOf`. This change fixes these tags for all JavaScript files in the wp-admin folder.

* Add jsdoc configuration to parse wp-admin/js files. Use `jsdoc -c jsdoc.conf.json` to generate JSDoc.
* Define all used namespaces using `@namespace`.
* Define each usage of the extend function as a prototype assignment using `@lends`.
* Add `@alias` if JSDoc cannot detect the correct name automatically.

This has previously been corrected for all `wp-includes` JavaScript files: [41351].

Props herregroen.
Fixes #42485.

Built from https://develop.svn.wordpress.org/trunk@42403


git-svn-id: https://core.svn.wordpress.org/trunk@42232 1a063a9b-81f0-0310-95a4-ce76da25c4cd