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.
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