* naively remove FSTPath import and source/test files.
* port FieldPath, part I
* port FieldPath, part II
* port ResourcePath, part I
* port ResourcePath, part II
* the grand commit to fix build errors
* use testutil:: helper instead of those from FSTHelpers
* fix test and lint
* use c_str in errmsg directly
* fix
* fix
* make code clean
* fix integration test I missed
* fix to avoid naming collision in preprocessor
* address changes
* address changes
* address changes
* fix: fieldMask are actually shared with different context.
* address changes
* add converter function between two DocumentKey implementations
* add unit test
* address changes
* fix lint
* 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
zxu