WIP: ext_external_objects/vk-stencil-display: new interoperability test that uses a Vulkan stencil buffer with OpenGL

The purpose of this test is to use a Vulkan stencil buffer from OpenGL. The test renders a quad with Vulkan and sets the stencil value to 1 for every pixel that is rendered. The stencil buffer is then imported in OpenGL and is used as the depth/stencil attachment of an OpenGL FBO. The color attachment of the FBO is cleared to green and is used as render target where a blue quad is rendered with the stencil test enabled and a stencil mask/reference combination that permits drawing only where the stencil value is 0. The final result must be a blue quad with a smaller green quad in the middle.