Native bindings to the OES_shader_multisample_interpolation extension.

In standard multisample rendering, an implementation is allowed to assign the same sets of fragment shader input values to each sample. This can cause aliasing where the fragment shader input values are used to generate a result that doesn't antialias itself, for example with alpha-tested transparency.

This extension adds the "sample" qualifier that can be used on vertex outputs and fragment inputs. When the "sample" qualifier is used, the fragment shader is invoked separately for each covered sample and all such qualified interpolants must be evaluated at the corresponding sample point.

This extension provides built-in fragment shader functions to provide fine-grained control over interpolation, including interpolating a fragment shader input at a programmable offset relative to the pixel center, a specific sample number, or at the centroid.

Requires GLES 3.0.