New read/write cases for integer types

Added new read/write functionality for integer types. Also added cases for integer types in some utility functions.

Change-Id: I5efc7c4957d3a1591b47a5df888a9534776033be
Reviewed-on: https://swiftshader-review.googlesource.com/4114
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>