Merge changes from topic "sync_enums_to_hal"

* changes:
  Replace sync_enums_to_hal.py with generate_api.{py,sh} and regenerate NeuralNetworks.h
  Document that PREFER_FAST_SINGLE_ANSWER is the the default execution preference
tree: 7e4283f0cf0552cea8fc05375158593a8a361966
  1. .clang-format
  2. CPPLINT.cfg
  3. CleanSpec.mk
  4. OWNERS
  5. PREUPLOAD.cfg
  6. nn/