Vulkan support

[hombit]

The future of the project is migration from OpenGL to Vulkan, or at least parallel implementation for the both framework.

Vulkan comes to Qt: QVulkanWindow and example, blog posts (1, 2).

Vulkan is supported by all major platforms. Linux has Mesa Vulkan support, macOS (and iOS) are supported via MoltenVK layer (is used by Qt), and Windows is supported by hardware drivers (as for OpenGL).

There are few Vulkan-related OpenGL extensions that could be useful in transition period, when we will write some code for Vulkan but still will have some OpenGL-only code: EXT_external_objects allows share Vulkan objects to OpenGL, i.e. use Vulkan object as OpenGL texture, NV_draw_vulkan_image allows draw Vulkan 2D image in OpenGL