Some subsystems are like conduits, passing data along to plugins which,
in turn, send the data externally. Only the component linking to (using)
the subsystem will know what data it is sending along to the eventual
external system, so should be able to specify this at the time of
linking. The same goes for plugintypes.
- Define sitepolicy handler manager class, base class and the core handler
- Allow to set a plugin as sitepolicyhandler that implements the sitepolicy API
- Modify web services to return information from the 3rd party handler instead of core if needed
This legacy polyfill allows plugin developers who release a single
branch to work with multiple versions of Moodle to support the API in
both Moodle 3.3 with PHP 5.6, and later versions.
