Introduce gmock matchers for TensorFlow nodes

I need these to write readable unit tests for TF graph transformations.  All of
my use cases will live inside tensorflow/compiler so putting it in
tensorflow/compiler/jit for now; but we can move these out if other users are
interested.

In the future we may want to auto-generate type safe versions of these from the
op registrations like we generate C++ wrappers today.

PiperOrigin-RevId: 213186810