Add static methods to `Float` that convert between the bit representation of a half precision floating point (float16) value and float.

The bit representation of a float16 value is a short value.

These methods will enable superior interoperation with machine learning models and native machine learning libraries.

The implementations will conform to the IEEE 754-2008 standard.

Additional work beyond the scope of this issue can improve the performance of these implementations:
- they can be made intrinsic leveraging hardware instructions on appropriate platforms; and 
- if the hardware platform supports vector instructions it may be possible to enhance C2's auto-vectorizer