Expose `SimbodyMatterSubsystemRep::multiplyByPVATranspose` to `SimbodyMatterSubsystem` about simbody

[nickbianco]

Thanks @sherm1! I agree, I think multiplyByPVTranspose makes more sense. I'll work on an implementation and some unit tests.

[sherm1]

Than, Nick! I think I didn't expose the general PVA function because of its awkward interface and complicated description -- instead I used it to implement simpler APIs. I wouldn't object to exposing it, but it might be cleaner just to add a function multibodyByPVTranspose() to the public API since we now know that's useful! Then you would only have to document that in the same manner as multibodyByGTranpose() with the implementation similar but (true,true,false) rather than all true. There should be a unit test or two to make sure it doesn't get broken in the future -- that would also be easier with a PV API than the general one.

I would welcome a PR adding this nice functionality!