Merge branch 'reverseplatform_clipping' into 'next'

FF_REVERSEPLATFORM clipping

Ran into an issue whilst testing out one last feature (there's always one more...) for flat_alignment_revamp. This is a backported fix.

The bug was such that if you're falling through a platform with FF_REVERSEPLATFORM and not FF_PLATFORM, you'll be pushed downwards such that your head is against the bottom of the FOF. This just checks momz is greater than zero if it has FF_REVERSEPLATFORM to make sure it's okay to set ceilingz. (OR the alternative in reverse gravity.)

No test map because this was originally done for internal. Instead, test it on the other branch's test map.

See merge request !83