Added constant folding for:
rad, deg, sin, cos, tan, asin, acos, atan, sinh, cosh, tanh,
asinh, acosh, atanh, log, log2, exp, exp2, sqrt, inverstsqrt

Change-Id: Ifc6b089e5981da9a3739d4ed7636953a682ce220
Reviewed-on: https://swiftshader-review.googlesource.com/5200Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>