Add targetElementRecord to before/after move element in structure function and events

[engram-design]

I have a use case where my element needs validation rules when moving it within a structure. See verbb/navigation#359 where I want to enforce user-defined rules on how many nodes for a particular level there can be.

Fortunately, I can use the Element::beforeMoveInStructure() function (or the Element::EVENT_BEFORE_MOVE_IN_STRUCTURE event if I wanted) to trigger validation with element->validate(). However, one glaring issue is that I cannot get the to-be-moved element information from the function or event, because it's not passed to it.

For example, if I want validation rules to check if something can be placed at level 2 if something is currently at level 1, there's no way for me to know what the new level will be, until after the fact. I only know about the level of it currently.

This information can be grabbed from $targetElementRecord.

Happy to revise this, or let me know if I've gone about this the wrong way.

[brandonkelly]

A breaking ElementInterface method signature change like this would need to wait until 5.0.

Adding additional properties to the MoveElementEvent class would be OK though (used by the EVENT_BEFORE_MOVE_ELEMENT and EVENT_AFTER_MOVE_ELEMENT events on the Structures service, where all the target element info is already known). So I’ve just added $action, $targetElementId, and getTargetElement() to that, for Craft 4.5 (#13429).

Also decided to deprecate Element::beforeMoveInStructure() / afterMoveInStructure() and the events they trigger, since they’re a little inconsistent with the service events (they get called/triggered for moves and inserts), and now the service events are more capable, so we should be steering people toward those.

[brandonkelly]

Craft 4.5.0 is out with those new events.