TFLM: Add ONE_HOT operator and unit tests

[junseokShim]

This PR adds ONE_HOT operator support to TensorFlow Lite Micro.

• Ported ONE_HOT kernel from TensorFlow Lite to Micro:
  • tensorflow/lite/micro/kernels/one_hot.cc
  • tensorflow/lite/micro/kernels/one_hot.h
• Added micro tests converted from Lite tests:
  • tensorflow/lite/micro/one_hot_test.cc
• Verified with:
  • make -f tensorflow/lite/micro/tools/make/Makefile test_one_hot_test
  • clang-format and cpplint.py on modified files

This intends to address #3078.

bug=fixes #3078

[google-cla]

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[junseokShim]

@googlebot I signed it!

[ddavis-2015]

@junseokShim Please add a line at the end of your PR description above: bug=fixes #3078. The CI will not pass without this line in the description.

[ddavis-2015]

@veblush Before this PR can be accepted, the LiteRT code will need to be updated to separate out the parameter parsing for ONE_HOT here . Operators that have individual parameter parsing methods are in the same file, located near the beginning of the file.

[ddavis-2015]

@junseokShim This does not seem to be a completed PR. Please adhere to the requirements as listed in issue #3078.

[junseokShim]

@junseokShim This does not seem to be a completed PR. Please adhere to the requirements as listed in issue #3078.

OK, I will double-check the detailed requirements and make sure they are reflected.