BulletSim: enable GImpact shape for prims with cuts. Include DLLs and SOs
which recompute GImpact shape bounding box after creation as Bullet
doesn't do that itself (something it does for nearly every other shape).

Now, physical prims without cuts become single mesh convex meshes. Physical
prims with cuts become GImpact meshes. Meshes become a set of convex
hulls approximated from the mesh unless the hulls are specified in the
mesh asset data. The use of GImpact shapes should make some mechanical
physics more stable.
BulletSim: default using mesh asset hulls to 'true'. This means that,
if the mesh asset specifies physics hulls, BulletSim will fetch and
use same rather than approximating the hulls. If physics hulls are not
specified, the representation will fall back to the regular physics mesh.