Improved some `BoatEntity` mappings.

[supersaiyansubtlety]

• checkBoatInWater -> isInWater; conventional and consistent with Location.IN_WATER
• checkLocation -> updateLocation; a bit of an odd one, updateLandFractionAndGetLocation would be a verbose literal name, I think updateLocation communicates that reasonably well
• landFriction -> groundFriction; to match getGroundFriction

I considered renaming all ground -> land in BoatEntity to be consistent with Location.ON_LAND, but Entity.fall's onGround param traces back to a string, so they can't be completely reconciled, and ground is used more in other classes and I think is slightly better in most cases.

[github-actions[bot]]

🚀 Target branch has been updated to 1.20.5

[github-actions[bot]]

🚀 Target branch has been updated to 1.20.6-rc1

[github-actions[bot]]

🚀 Target branch has been updated to 1.20.6