Removed registry for benchmark reports & introduced benchmark_config.{h,cc} in the spirit of test_config.{h,cc}.

The purpose of benchmark_config is to allow for different behaviors to
be decided at compile-time.

It now allows pluggging in "reporter" instances to process the benchmark results arbitrarily.
This would allow, for example, to send results to a leaderboard and/or other systems for tracking performance metrics.

Add a GrpcLibrary class to wrap grpc_init and grpc_shutdown and convert all the tests to init/shutdown free.

This allows us to get back to single binary tests where appropriate, which will help in-depth profiling efforts.
I've built this atop my smoke_test changes as they inspired me to get this done.

-) using dupenv_s instead of getenv_s and calling strdup ourselves.
-) few impossible-to-obtain if checks.
-) various signed/unsigned casting.
-) using time_t instead of time32_t
-) checking output of FormatMessage for failures.
-) don't redefine _WIN32_WINNT without undefining it first.
-) fixed msvc's interlocked casting.
-) renamed AddPort to AddListeningPort.
-) added protobuf's third_party includes to search path.
-) added a missing definition for inet_ntop in mingw32.
-) removed useless declarations.

Now setup as a driver and N anonymous workers that may become clients or servers.
Will convert async soon.