This aligns CI Windows builds with recently shipped deps to support AV1
and RIST as well as providing other updates.
* Update FFmpeg from 4.2.4 to 4.4.1
* Update nv-codec-headers from 9.0.18.2 to 11.1.5.0
* Add libaom and SVT-AV1 support (64-bit only)
* Add RIST support
* Enable multithreading for libvpx obs-deps builds