- cleanup of the virtual function definitions for inventory items. Let's better use 'virtual' and 'override' everywhere to make sure that nothing gets overlooked.

- added call wrappers and script hooks for all relevant virtuals in AInventory.
- made GetSpeedFactor and GetNoTeleportFreeze entirely scripted because they are too trivial - also do them iteratively, just like HandlePickup, because it's just a better way to do this stuff.

src/d_dehacked.cpp

@@ -3157,7 +3157,7 @@ FString ADehackedPickup::PickupMessage ()
 bool ADehackedPickup::ShouldStay ()
 {
 	if (RealPickup != nullptr)
-		return RealPickup->ShouldStay ();
+		return RealPickup->CallShouldStay ();
 	else return true;
 }