ChunkGenerator - add getHeight to ChunkData

[ShaneBeee]

This PR aims to add an option to ChunkGenerator.ChunkData to get the current height.
This allows to get the height generated in a previous step.
For example, let's say I have a generator where I allow Minecraft to generate the noise, but I want to generate the surface.
I can get the height that was previously generated in the noise step, and plop my surface block on top of that in the surface step.

Closes #12048

[Lulu13022002]

A check for out of bound position might be nice like the other methods and then return 0 (or throw) to avoid unexpected value. And the first line of javadocs seems incomplete.

[ShaneBeee]

A check for out of bound position might be nice like the other methods and then return 0 (or throw) to avoid unexpected value.

Thats a good idea, thank you, good catch.

And the first line of javadocs seems incomplete.

Well that is embarrassing 😬

edit: updated! thanks again.

[kennytv]

I'd just throw if it's OOB and make the checks clearer with <0 / >15

[ShaneBeee]

I'd just throw if it's OOB and make the checks clearer with <0 / >15

Sounds good to me, thank you.
Changes have been made!