Uses the DROP_TO_FLOOR() engine function on an entity, which attempts to put
it down on the floor.
This engine function traces 256 units straight downwards from the
entity origin. If the trace hits the floor, the origin is updated to
the end position of the trace, FL_ONGROUND is added to the flags and
EV_ENT_groundentity is updated. When the trace does not hit anything or
the entity would be stuck inside something, the function does nothing
and returns 0.
1 if entity is on the floor, 0 otherwise