PyBullet-New feature: Allow composite convex hulls to be procedurally created

[neemoh]

Since #1926 it is allowed to pass vertices/indices to createCollisionShape instead of a file name, which is great. However, it is only possible to create a collision shape with a single convex hull, since the vertices are expected to be a list of Vec3.

In contrast, when reading from a .obj file the collision shape can have multiple convex hulls (coming for instance from the VHACD). It would be great to expose this to the Python API too. So one can pass a list[list[Vec3]] as vertices to createCollisionShape.