Add external image interop API
If a user has their own VkImage created from the same VkDevice (e.g. via hwdec interop), there's currently no public way to get that wrapped into a ra_tex
for consumption by libplacebo. This obviously needs to be remedied.
The appropriate function more or less already exists internally (ra_vk_wrap_swapchain_image
-> vk_init_image
). A similar function needs to be created for wrapping generic VkImages, perhaps even replacing the one specialized for swapchains, made public, and documented.
Some thought and research needs to be done in order to figure out the best API for this.