Add Combat Test as an Experimental feature (like the others)

I know you don't want to focus too much on a combat rework right now, but just like you changed the Minecarts or Villagers but not as a definitve thing, there should be an option to add everything introduced in Combat Tests Snapshots as Experimental features

This way, newer users could try these features and continue providing feedback, as well as allowing us to play on newer versions

And the best part: If you don't want to make any more changes yet, you can leave it as something to do in the future, and not worry about it too much