Levitation doesn't work underwater

Verification builds: Release 920093
Summary: The Minecraft effects "levitation" does not affect any mob underwater.

Repro Steps:

1. Stand in water, or summon a mob and put it underwater
2. do /effect @e levitation 10 10

Observed Results: You will not levitate

Expected Results: Indeed the current status quo is that levitation doesn't, and shouldn't work underwater and has in the past been listed as working as intended.

Impact: Currently the smoothest way to raise and lower mobs is through levitation, being unable to arbitrarily manipulate the height of mobs underwater impacts our ability to do this without janky as hell teleporting. If levitation is not able to, or wont, be fixed to work on mobs underwater, I propose a new effect "buoyancy" which would ONLY work on mobs underwater and make them rise to the surface, but not in the air.

This specific "bug" severely impacts the impact of a future project, if it isn't something that can be changed/added it will have to be rescoped into something significantly less impressive.