Expand Pose API

[SoSeDiK]

Adds a way to set entity's pose. Fixed pose can be changed/reset only via another API call. (my take on #7318 since it was closed))

Resolves #7016.

[MWHunter]

Other players will see the pose but the client will revert this immediately on the next tick. This seems hacky and PoseChangeEvent might be a better thing. There should also be warnings so people don't expect too much from poses.

[SoSeDiK]

Yep, poses work for entities and other players will see the pose correctly (and having it fixed won't let the player reset it next tick). Only the player with the pose applied to themselves won't be able to see it client-side. I left a note about this in javadocs,