PolyObject fixes backport

This branch backports some recently made fixes to PolyObject physics issues we were aware of in 2.2.

The following bugs are fixed:

• When riding a PolyObject platform following waypoints, and you decide to walk off the edge of the platform, you immediately teleport to the ground. This was linked to an earlier MR attempting to allow PolyObjects to crush players vertically IIRC, and my fix for this probably makes !422 (closed) redundant.
• If the PolyObject's outer control sector is not the same as that which the PolyObject is actually physically inside, it is possible to "collide" with thin air below or above the PolyObject, depending on the heights of the sectors involved.

"It builds"

merged

mentioned in commit 392cb89f

Note so I don't forget: PolyObjects with Crush spawn points don't seem to properly crush players sometimes with this fix, though I have discovered this lack of crushing can happen even in 2.1.24 if the outer control sector is not the polyobject's current location in-level. (I plan to look into this more tomorrow)

Nevermind I've got the fix now, it was rather simple even, ignore the comment I made last night.