* Drop acknowledged mutations in schema migration (#1818)
Drop acknowledged mutations in schema migration as part of removing held write acks.
Port of firebase/firebase-js-sdk#1149
* Change removeMutationBatch to remove a single batch (#1955)
* Update Firestore Generated Protos
* Adding UnknownDocument and hasCommittedMutations (#1971)
* Removing held write batch handling from LocalStore (#1997)
* View changes for held write acks (#2004)
* Held Write Acks Unit Test Fixes (#2008)
* Held Write Ack Removal Spec Tests (#2018)
* Fix integration test
Extract useful bits of FSTUserDataConverter for use in C++:
* Migrate FSTParsedSetData to core::ParsedSetData
* Migrate FSTParsedUpdateData to core::ParsedUpdateData
* Migrate FSTParseContext to core::ParseContext
* Split ParseAccumulator out of ParseContext to make ownership easier
Also:
* Remove dead code (handled in parseSentinelFieldValue)
* Flatten App/iOS/Supporting Files into the parent
* Move all Firestore files to Objective-C++
* Update project file references
* Don't use module imports from Objective-C++
* Use extern "C" for C-accessible globals
* Work around more stringent type checking in Objective-C++
* NSMutableDictionary ivars aren't implicitly casted to NSDictionary
* FSTMaybeDocument callback can't be passed a function that accepts
FSTDocument
* NSComparisonResult can't be multiplied by -1 without casting
* Add a #include <inttypes.h> where needed
* Avoid using C++ keywords as variables
* Remove #if __cplusplus guards
Gil