Added some "low hanging fruit" implementations and quick validation
checks for a portion of the GLES 3.0 API functions.

Change-Id: I003031091bc2c2c32919896e86e38b5f1f43c555
Reviewed-on: https://swiftshader-review.googlesource.com/2610Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>