move Import Processor plugins and Client Authorization plugins into common parent folder

Problem/Motivation

It's confusing to have Client Authorization plugins in

- /src/Plugin/ClientAuthorization/Anonymous.php

and processor plugins in:

- /src/Plugin/EntityShareClient/Processor/BlockFieldBlockContentImporter.php

Steps to reproduce

Proposed resolution

Move both plugin types into a common parent folder, similarly to how it's done in core modules like views and migrate, the core Field component, or the search_api contrib module.

Remaining tasks

User interface changes

API changes

Data model changes