We should only generate delegates for actual OpenGL entry points, not for overloaded functions that resolve to the same entry point. This improves loading speeds and reduces the size of the compiled dll.
Khronos renamed BeginMode to PrimitiveType starting with GL 4.4. OpenTK now has overloads for both flavors.
Large code-drop from Khronos upstream.
The new bindings are based on the fresh gl.xml registry by the Khronos group.