Please make opencv-python-headless support FFmpeg 9.0

Start by inspecting opencv/modules/videoio/src/cap_ffmpeg_hw.hpp around line 760 and cap_ffmpeg_impl.hpp around line 2586, then reproduce the headless build against FFmpeg 9.0. Check the relevant FFmpeg API changes and verify that the build completes without the reported AVCodec member errors.

Errors:

[ 80%] Building CXX object modules/videoio/CMakeFiles/opencv_videoio.dir/src/cap_ffmpeg.cpp.o
In file included from /wrkdirs/usr/ports/graphics/py-opencv-python-headless/work-py312/opencv-python-92/opencv/modules/videoio/src/cap_ffmpeg.cpp:50:
In file included from /wrkdirs/usr/ports/graphics/py-opencv-python-headless/work-py312/opencv-python-92/opencv/modules/videoio/src/cap_ffmpeg_impl.hpp:175:
/wrkdirs/usr/ports/graphics/py-opencv-python-headless/work-py312/opencv-python-92/opencv/modules/videoio/src/cap_ffmpeg_hw.hpp:760:82: error: no member named 'pix_fmts' in 'AVCodec'
  760 |             if (av_codec_is_encoder(c) && hw_native_fmt != AV_PIX_FMT_NONE && c->pix_fmts) {
      |                                                                               ~  ^
/wrkdirs/usr/ports/graphics/py-opencv-python-headless/work-py312/opencv-python-92/opencv/modules/videoio/src/cap_ffmpeg_hw.hpp:761:36: error: no member named 'pix_fmts' in 'AVCodec'
  761 |                 for (int i = 0; c->pix_fmts[i] != AV_PIX_FMT_NONE; i++) {
      |                                 ~  ^
/wrkdirs/usr/ports/graphics/py-opencv-python-headless/work-py312/opencv-python-92/opencv/modules/videoio/src/cap_ffmpeg_hw.hpp:762:28: error: no member named 'pix_fmts' in 'AVCodec'
  762 |                     if (c->pix_fmts[i] == hw_native_fmt) {
      |                         ~  ^
In file included from /wrkdirs/usr/ports/graphics/py-opencv-python-headless/work-py312/opencv-python-92/opencv/modules/videoio/src/cap_ffmpeg.cpp:50:
/wrkdirs/usr/ports/graphics/py-opencv-python-headless/work-py312/opencv-python-92/opencv/modules/videoio/src/cap_ffmpeg_impl.hpp:2586:24: error: no member named 'supported_framerates' in 'AVCodec'
 2586 |     if(codec && codec->supported_framerates){
      |                 ~~~~~  ^
/wrkdirs/usr/ports/graphics/py-opencv-python-headless/work-py312/opencv-python-92/opencv/modules/videoio/src/cap_ffmpeg_impl.hpp:2587:37: error: no member named 'supported_framerates' in 'AVCodec'
 2587 |         const AVRational *p= codec->supported_framerates;
      |                              ~~~~~  ^
5 errors generated.
*** Error code 1

Downstream bug report: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=297370