This is a first (somewhat non-intuitive) step towards being able to use
clang as part of the github CI system.
The benefits of this refactor are that we avoid a dependency into
tensorflow/core which reduces the number of files that need to be
downloaded as part of a bazel build from a TFLM CI docker image.
The tflite schema version has been unchanged since at-least Oct 2018
(when tflite was moved out of tensorflow/contrib).
Progress towards preventing a repeat of https://github.com/tensorflow/tensorflow/issues/46415
4dadd12623