Use typedef to represent storage type in FPOption and FPOptionsOverride

Size of FPOption is now 14 bit, which is closed to the current limit
of 16 bits. Adding new properties to FPOption would require change of
the types, which represent storage of FPOption and FPOptionsOverride.
To facilitate this change, the storage types were changed from standard
integer types to typedefs defined inside the proper classes. Checks for
size of these storage types were added.

No functional changes intended.

Differential Revision: https://reviews.llvm.org/D84147