* Revert "Revert "gRPC: replace Objective-C implementation with the new C++ implementation (#1968)" (#2030)"
This reverts commit ea567dca47.
* gRPC: fix bugs found during testing (#2039)
All in `GrpcStream`:
* make sure there are no pending completions when "finish" operation is enqueued;
* always finish gRPC calls;
* when connectivity changes, reset not just the calls, but the underlying channel as well.
* Revert "Partially revert "Update CHANGELOG for Firestore v0.14.0 (#2025)" (#2031)"
This reverts commit b2437b80f6.
* Update changelog for v0.15.0.
* gRPC: add gRPC wrapper classes to CMake build (#2015)
* add a C++ equivalent of `FIRFirestoreVersionString`. This eliminates the only Objective-C dependency of `grpc_connection.mm` and allows making it a pure C++ file;
* open-source `binary_to_array.py` script and use it in the build to embed `roots.pem` certificate file from gRPC into the Firestore binary. The embedded char array is then used to load certificate at runtime.
* Revert local change -- do not enable sanitizers by default
