[1.21.x] Added ShapeUpdateEvent

[ZygZagGaming]

This PR adds a ShapeUpdateEvent called whenever a block's shape changes. This allows modders to detect updates that are caught by observers but not by BUDs, meaning they don't call NeighborNotifyEvent. For example, this event is called on trapdoor, door, and fence gate closing/opening, as well as fence, wall, and iron bar shape changes.

I made this PR because I need an event like this in my own mod, and I think it could be helpful for other modders to have.

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[marchermans]

Allthough I generally approve of the event, I am a bit confused about the events description.

Does this detect trapdoor toggling or not?

[Technici4n]

Might want to be careful with performance here.

[ZygZagGaming]

Allthough I generally approve of the event, I am a bit confused about the events description.

Does this detect trapdoor toggling or not?

Apologies for the confusion. Yes, this does. It essentially detects every change an observer would detect, versus NeighborNotifyEvent, which detects only changes a traditional BUD would detect.

[ZygZagGaming]

Might want to be careful with performance here.

I thought about that when writing this PR; however, I don't see a way to optimize this without compromising the intent of the event.