Gamerules to keep xp or potion effects on death

I think new gamerules called keepexp and keepeffects should be added, which keep your experience levels or potion effects on death.

We already have keepinventory, and these are the only two other things you lose when you die. Sometimes it can be a hassle to lose a bunch of xp if you die, so this would remove that.

Of course they would be off by default, but anyone could turn them on, just like keepinventory, if they want an easier time playing the game.