This involves a large amount of change in test scene setup code to allow test scenes to share shared modules
SetupScene is now an instance method that requires an instantiation of SceneHelpers, though other SceneHelpers methods are still static
May split these out into separate classes in the future.
This was an oversight when removing some race conditions from PhysicsActor setting recently.
Regression tests extended to probe this code path.
Extending regression tests required implementation of a BasicPhysicsPrim (there was none before). However, BasicPhysics plugin is still of no current practical use other than to fill in as a component for other parts of regression testing.
On region restart, the whole object would become physical as expected.
Observed behaviour from elsewhere is that all prims in a new linkset should take on the status of the root prim.
Add regression test for this behaviour.
