* use vcpkg to install ffmpeg and build sdk from source, so no prebuild lib in hwcodec.
* link ffmpeg in rustdesk directly, ffmpeg can be used as basic library.
* for windows developers, `VCPKG_DEFAULT_HOST_TRIPLET` env need to be set to `x64-windows-static` during installation.
Signed-off-by: 21pages <sunboeasy@gmail.com>