Texture sharing between OpenGL and Vulkan on macOS

[llfab]

We are using AvaloniaUI (https://github.com/AvaloniaUI/Avalonia) as a cross-platform UI technology. We have integrated our own vulkan based 3D renderer while running Avalonia on OpenGL. This is done using

"VK_KHR_external_semaphore_win32",
"VK_KHR_external_semaphore",
"VK_KHR_external_memory_win32",
"VK_KHR_external_memory"

on Windows and the corresponding external functions on Linux to allow for shared textures. By doing so, we allow for our 3D renderer to create a vk texture in the GPU memory and pass this to the Avalonia renderer without downloading it into CPU and re-uploading it into GPU again.

Hence, I wonder what would be a viable path. I did see #316, however this does not fully tackle my point.