[Suggestion] Expose setting level through commands

[jaimejaime19]

There is a command that adds a level and another that gets the level. I see in the add code that you can set the level directly. This would be extremely useful for adding the setter commands to items to manually increase or decrease the level by a dev-chosen amount.

PS I tried to make a PR for this but I could not figure out why the game would crash when starting a new world. Definitely a dev thing though.

[jaimejaime19]

@Daripher I made a PR for this command as well as adding a fix for a crash on 1.20 when loading into a world.