BattlePokemon#runImmunity is now two functions, runImmunity and
runStatusImmunity.
The split is helpful because: 1. NegateImmunity only applies to type
immunities, and 2. Immunity only applies to status immunities and
Ground immunities.
Ground immunities are now entirely handled hardcoded in isGrounded.
This overall doesn't have a noticeable impact on performance, but
it makes certain things behave more predictably, and correctly
shows the ability activation for Levitate, so I assume that means it's
a net positive. I hope I at least improved readability...