Including a bunch of BitFields additions so we can get the desired
codegen without sacrificing readability or flexibility.
(The alternative would be building masks and masking manually.)
getCollisionFilterInfo was changed to return a u32 instead of
EntityCollisionFilterInfo because a collision filter info mask
can be either an EntityCollisionFilterInfo or a ReceiverMask.
(Also at some point we'll probably want to rename
EntityCollisionFilterInfo because that is also used for sensor
rigid bodies and not just for entities.)
It was called MemSystem in the IDB because of a string in
ksys::InitializeApp that referred to MemSystem initialisation as
"Physics Memory System"; however that string actually referred to an
initialisation step for the physics system, not to the name of the
subsystem itself.
Léo Lam