Add VA-API adaption to enable video hardware acceleration in WSL2

[seflerZ]

Here the WSL2's GPU-PV has implemented VA-API API. I've noticed that our recent dev branch has implemented software x264 and nvenc hardware encodings. I hope libva can be added to increase x264 frame encoding speed. @jsorg71

[Entropy512]

Not just WSL2 - any non-Nvidia GPU, or even many use cases of paravirtualization under an NVidia GPU such as venus and dxgkrnl. Especially since vaapi also works for nvidia GPUs.

[YinlinHu]

A good example of how VAAPI is used in 264 encoding and decoding on both NVIDIA and Non-NVIDIA GPUs: https://github.com/LizardByte/Sunshine