APIv4 - Deprecate Entity::getLinks action

[colemanw]

Overview

Deprecates an obscure APIv4 action which was only used in one place (the Explorer).
Updates the APIv4 Explorer to not use it and to display it as deprecated.

Technical Details

The action returns a bunch of deprecated information which is not useful.
The APIv4 Explorer had been using a small portion of the info which was actually redundant with existing info from getFields.

[civibot]

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[eileenmcnaughton]

OK - I definitely can''t see any more getlinks calls going on in universe - I'm struggling to make sense of the removed getBackReferences function to agree or not agree on removing that.

[colemanw]

I'm struggling to make sense of the removed getBackReferences function to agree or not agree on removing that.

When APIv4 was in its infancy there was a very different idea about how joins would work, which involved a second query behind-the-scenes to fetch e.g. multiple activities per contact, and a syntax like 'select' => ['contact.activities.subject']. That's all been ripped out in favor of the new explicit join syntax, so these backreferences to generate links like "contact.activities" are obsolete and unused. Currently it's just wasting CPU cycles every time you call the api.

[eileenmcnaughton]

OK @colemanw