combine more core batch ops

Stress test framework design document

Don't set up Python doc packages every time

Move method_config module from ext/client_channel to lib/transport.

Plumb channel_args through resolvers.

Make ServerCallContext.Peer lazy

C#: SafeHandleZeroIsInvalid cleanup

New python interop tests

Introduce a grpc-exp ALPN protocol identifier.

Flush ObjC cached channels when network connectivity changes

Updated C_PYTHON_DEV_ERROR_MESSAGE err msg w/RHEL+Fedora

Add a libuv endpoint to the C core, for use in the Node library

Add the code for three new interop tests: unimplemented_method,
unimplemented_service, and custom_metadata.

Fix and refactor the code for status_code_and_message.

The node interop client was checking that the status message for
the test unimplemented_method was an empty string. This behavior
is not guaranteed, and thus the check should be removed.

Implement PHP Unimplemented Method Interop Test