ChunkUnloadEvent#setSaveChunk doesn't affect saving entity chunk

[GliczDev]

Is your feature request related to a problem?

Currently, ChunkUnloadEvent#setSaveChunk doesn't affect saving entity chunk, while it does affect chunk and poi chunk.
This is intended, however it still would be useful to abort saving the whole chunk with all its data.

Describe the solution you'd like.

I propose 3 solutions

1. (best) Deprecate ChunkUnloadEvent#setSaveChunk and allow specifying which chunk parts/types should not be saved.
   For example:

// note: this is usage example, method/class naming is subject to change
@EventHandler
public void onChunkUnload(ChunkUnloadEvent e) {
    // to skip entity chunk saving:
    e.setSavedParts(ChunkUnloadEvent.ChunkPart.CHUNK, ChunkUnloadEvent.ChunkPart.POI_CHUNK);

    // to skip poi chunk saving:
    e.setSavedParts(ChunkUnloadEvent.ChunkPart.CHUNK, ChunkUnloadEvent.ChunkPart.ENTITY_CHUNK);

    // to skip poi chunk and entity chunk saving
    e.setSavedParts(ChunkUnloadEvent.ChunkPart.CHUNK);
    
    // to not save anything
    e.setSavedParts(); // tho I don't really like how it looks. maybe some kind of `disablePartSaving`/`enablePartSaving` would be better?
}

Even tho poi chunks are not exposed in the API, they are still part of the game and not saving them still somehow affect it.
Eventually separate events for chunk, poi chunk and entity chunk unloading would also work.

2. (good) make ChunkUnloadEvent#setSaveChunk also not save entity chunk.

3. (ok, but personally I don't like it) better document ChunkUnloadEvent#setSaveChunk method that it does not affect entity chunk saving.

Describe alternatives you've considered.

Using EntitiesUnloadEvent and removing all entities, tho this event doesn't feel like it was intended for it

Other

Most of the proposed solutions require moonrise modifications. After discussion on the discord, I've decided to open this discussion here first, because it still kinda feels like a flaw in the API, tho personally I'm curious about the implementation (moonrise) choices.

If this idea gets accepted (especially my proposed solutions 1 and 2), I am willing to make a PR implementing it to both Paper and Moonrise repository (as both require changes)