Added entity middle-click feature

[JavierLeon9966]

Introduction

Added entity middle-click feature, this is a vanilla feature that it hasn't been implemented for so long.

Relevant issues

• Closes Add a PlayerEntityPickEvent #4766

Changes

API changes

Added the following methods in Entity:

• Entity->getCleanedNBT(): Returns a cleaned NBT from the entity, removing tags such as position, motion, etc.
• Entity->copyDataFromItem(): Copies the entity NBT from the item into the entity (internal).
• Entity->getSpawnItem(): Returns the item that can be used to spawn the entity, by default it returns air if there isn't one.
• Entity->getPickedItem(): Returns an item that is able to spawn said entity, with a parameter $addUserData to include the entity's NBT.

Added the following methods in Item:

• Item->clearCustomEntityData(): Clears the NBT from the picked (middle-clicked) entity.
• Item->setCustomEntityData(): Sets the NBT of the picked (middle-clicked) entity.
• Item->getCustomEntityData(): Returns the NBT of the picked (middle-clicked) entity.

Added the following method in Player:

• Player->pickEntity(): Equips the middle-clicked (picked) entity in the player's hand with added NBT if requested.

Added the following event:

• PlayerEntityPickEvent

Tests

https://clipchamp.com/watch/nrP09ZXooey

[dktapps]

I'd prefer this wasn't dependent on NBT. Bad enough that we have to deal with that for tiles already...

[dktapps]

I don't like that this involves so much in the way of legacy hacks.

[dktapps]

I'm hesitant to merge this because entities currently predominantly use the Java entity NBT format, but items use the Bedrock format. This is already a disaster for tiles.

I'm OK with having the basic entity picking, but I think the NBT stuff should be removed for now until the internals handling can be cleaned up (and preferably find a way to deal with extra data that doesn't require NBT at all).

[dktapps]

The separation between "spawn item" and "picked item" seems redundant.

[jasonw4331]

@JavierLeon9966 any updates for this PR? If not it will be closed when API 5 releases

[JavierLeon9966]

Oh, whoops, I forgot about it, but I think I have the changes in my local

[dktapps]

This looks basically fine as it is right now, minus a few nits.

I will mention that we'll probably want to apply #4771 to PlayerEntityPickEvent too, but that's a problem for another time. The most important thing is for the events to be consistent.