Add explicit type support for bitfieldReverse (#4174)

This was missing for 8- and 16-bit types.

* Add unit tests for bit operations with 8/16-bit types

This adds tests for bitfieldExtract, bitfieldInsert, bitfieldReverse,
bitCount, findLSB, and findMSB with arguments of explicitly sized
8-bit and 16-bit signed and unsigned integers.

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Co-authored-by: Graeme Leese <gleese@broadcom.com>

Author: arcady-lunarg