Support interoperability with OpenGL textures

[jherico]

Developers who want to migrate to Vulkan and MoltenVK may still depend on external libraries that only work with OpenGL, or may want to do their work piecemeal. Being able to share textures between Vulkan and OpenGL is critical to these developers.

On other platforms, the VK_KHR_external_XXX extensions (and the corresponding GL_EXT_external_objects extension) allow this. However, this is obviously a non-starter on MacOS since you can't inject into the native OpenGL context.

But Apple documentation does show that it's possible to share image memory between Metal and OpenGL, and thus in theory there should be a way to share it between OpenGL and a Vulkan implementation running on top of Metal

[awkr]

I'm looking forward to this too !!!