Fixes VTS test failures.

Moves comments for type range values into their enums to make it harder
to forget to update them.

Adds missing float16 types for ARGMAX/ARGMIN/CAST.

Test: VtsHalNeuralnetworksV1_2TargetTest --hal_service_instance=android.hardware.neuralnetworks@1.2::IDevice/sample-all
Test: [  PASSED  ] 2519 tests.

Change-Id: Ic7c3df8c8fbff45fe497f304b6b2c7a09e7dc5a6