Native bindings to the ARB_enhanced_layouts extension.

This extension adds the following functionality to layout qualifiers, including broadening the API where this functionality is reflected. The following are added:

1. Use compile-time constant expressions.
2. Specify explicit byte offsets within a uniform or shader storage block.
3. Force alignment within a uniform or shader storage block.
4. Specify component numbers to more fully utilize the vec4-slot interfaces between shader outputs and shader inputs.
5. Specify transform/feedback buffers, locations, and widths.
6. Allow locations on input and output blocks for SSO interface matching.

Requires OpenGL 3.1 and GLSL 1.40. Promoted to core in OpenGL 4.4.