qt: probe d3d12 before d3d11 on windows

Since the probe result is cached, we don't have performance impact at each startup as probing is done asynchronously with its result being respected for the next startup.

This means that we don't have anything to lose by probing d3d12 first, which makes more sense to use if available compared to d3d11.

The video integration has already been tested.

Note that on Windows 7, even if DirectX 12 is installed d3d12 is not usable as RHI also uses Direct Composition with it where it is not available on Windows 7. So, this is mainly relevant for Windows 8/10/11.

D3D12 can use the already provided HLSL 5.0 shaders, so we don't need to necessarily provide HLSL 6 shaders for it to work. Although ideally the latest version should be provided, that is handled in a different commit.

Based on !6818.

Request review @chub.