OpenCV Windows video plugin: retained publisher source material

The original publisher archives and supplemental original source are retained
unmodified. The publisher commit is 664c0098dcb47b361f20c1d6a518653c23f5f2b5.

The publisher's sources/opencv_ffmpeg.tar.xz contains the build recipes but an
empty OpenCV submodule. Restore its opencv directory from
full-source/opencv-a0a660fcb1e58a295e6caa6aee64ed4d369b0181.tar.gz, removing that archive's first
directory component. The retained build_videoio_plugin.sh expects /build/opencv
and modules/videoio/misc/plugin_ffmpeg, plus the core, imgproc and videoio sources.
Restore the AOM, FFmpeg and libvpx source archives into the build directories
used by the retained recipes. Their licences and patent notices remain intact.

The publisher's OpenH264 API archive is empty because its archive script uses
the retired codec/api/svc directory. Cisco v2.5.0 has those headers in
codec/api/wels. For the retained BUILD_SKIP_DOWNLOAD_SOURCES offline branch,
copy the four original codec*.h files from OpenH264/codec/api/wels to
build/openh264/codec/api/svc. Preserve OpenH264/LICENSE. The original API source
commit is 8c7008aeb6335e7d36ab0d9a023a63f82a8eaac0. No OpenH264 codec implementation or DLL is
distributed by this Oro collector.

Use the retained build/env.sh, docker/Dockerfile and ffmpeg build scripts for
the publisher's compilation environment and settings. These materials supply
the reviewed source inputs; this collector does not execute a native rebuild
or claim a bit-identical reproduction of the publisher's binary.
