"MobjHitFloor" and "MobjHitCeiling" hooks
This MR adds two new hooks for Object floor and ceiling collision. Returning true
on a non-player Object marks it as killed/exploded/removed, while returning false
doesn't. In both cases, the default behavior is overridden. Returning nil
runs the hook alongside the default behavior for the Object type.
These hooks only work for Objects that don't have the MF_NOCLIPHEIGHT flag set.
Test Lua script: MobjHitFloorTest.lua