GL_HALF_FLOAT and GL_HALF_FLOAT_OES
do not have the same value, so to
be able to support GL_HALF_FLOAT
(in OpenGL ES 3.0) the same way we
used to support GL_HALF_FLOAT_OES
(in OpenGL ES 2.0), a few spots in
the code need to handle both cases.

Change-Id: I1fa60c51c65d693f5cc45124cd71411320f24014
Reviewed-on: https://swiftshader-review.googlesource.com/3192Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>