Remove pimpl class from PassRegistry.
Since removeRegistrationListener is no longer called during static destruction, we can get rid of the pimpl in PassRegistry.
This should clean up the code somewhat, increase clarity, and also allows us to put the Lock as a member of the class, instead of as a ManagedStatic.
As part of this change, the PassInfo class is moved from PassSupport.h to its own file, to eliminate the otherwise circular header dependency between PassRegistry.h and PassSupport.h
I take it you had to split this out to resolve a dependency that wasn't exposed when everything was pmpld away?