tflite: generate flatbuffers files from schema with flatc

currently the generated flatbuffer files are checked-in to tensorflow source.
this breaks builds with unbundled flatbuffers on any version mismatch,
because flatc-generated headers have static_asserts checking if same version
of library and flatc is used.

Bug: https://github.com/tensorflow/tensorflow/issues/62298
Change-Id: Ie4ed9b2683acdb850e35b3861fcfbc4828f536e7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5595037


Commit-Queue: Elly FJ <ellyjones@chromium.org>
Reviewed-by: Sophie Chang <sophiechang@chromium.org>
Reviewed-by: Elly FJ <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1312988}