Smart `cast` operation

[dmlloyd]

People are frequently tripping over casting, because primitive casts, object casts, and boxing/unboxing are all done in different ways. Provide a smart cast operation with the following support:

• Cast primitives to primtives as per convertPrimitive
• Cast objects to objects as per checkCast

And optionally:

• Cast primitives to primitive box objects by doing primitive-to-primitive conversion (if necessary) followed by BoxType.valueOf(...)
• Cast primitive box objects to primitives by doing BoxType.xxxValue() followed by primitive-to-primitive conversion (if necessary)
• Cast box objects to box objects by unboxing, converting, and then re-boxing

Since checkCast allows a String argument, primitive types and box types would need to be recognized by name.