[v4.4/v4.2] Minimize work under CollectionCatalog mutex

The CollectionCatalog mutex can be a source of contention. There are some minor improvements that can be done without changing how the system works at a high level.

1. Hash namespace/uuid without holding the lock
2. Add interface to match call patterns. RequiresCollectionStage::doRestoreState makes two calls (requiring taking and releasing the mutex twice) for something that can be implemented as a single call.