To avoid duplicating code, Float4(RValue<Byte4>) and Float4(RValue<SByte4>) now call Int4(RValue<Byte4>) and Int4(RValue<SByte4>) respectively.

Change-Id: Ic49fdd151d15cc1c2753f535d3654028e7a1910a
Reviewed-on: https://swiftshader-review.googlesource.com/5560Tested-by: Meng-Lin Wu <marleymoo@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>