* Port FSTMemoryPersistence to C++ (#3754)
* Add local::Persistence
* Add MemoryPersistence
* Add MemoryEagerReferenceDelegate
* Make LruDelegate extend ReferenceDelegate
This enables downcasting to LruDelegate in tests that need to do so.
* Add MemoryLruReferenceDelegate
* Don't double-count document key size.
* Port FSTLevelDB to C++ (#3755)
* Add LevelDbPersistence
Note that Apple-specific initialization has been partitioned off in
anticipation of being able to run this code on non-Apple platforms.
* Add LevelDbLruReferenceDelegate
* Migrate to C++ Persistence (1/2) (#3756)
* Use C++ Persistence classes in FSTLocalStore
* Remove ReferenceDelegateBridge
* Cut src over to C++ persistence types
* Remove Objective-C requirement from some classes
... that no longer require it.
* Migrate to C++ Persistence (2/2) (#3757)
* Remove LruDelegateBridge
* Update test initialization of persistence components
In particular, ensure that there's always an owner for the Persistence
instance, which wasn't always handled explicitly in the Objective-C
version of the tests.
* Largely mechanical changes to tests
* Remove Objective-C persistence classes
* Forward declare util::Status when possible (#3761)
* Add a header dedicated to forward declarations for util::Status
* Use status_fwd.h wherever possible
Gil