[SPIRV] Fix OpConstant float and double printing

Print OpConstant floats as formatted decimal floating points, with
special case exceptions to print infinity and NaN as hexfloats.

This change follows from the fixes in
https://github.com/llvm/llvm-project/pull/66686 to correct how
constant values are printed generally.

Differential Revision: https://reviews.llvm.org/D159376