T192307: Provide MCR-aware hook points

Phabricator Link	T192307
Status	open
Priority	normal (orange)
Author	[1]
Owner
Projects	Multi-Content-Revisions (Tech Debt) CPT Initiatives (MCR)
Subtasks	T205982: MCR: replace PageContentSave hook: must have a hook that receives all slots (for edit-intercepting extensions like Moderation)
Parent Tasks	T196087: Refactored implementation of MCR page update interface
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