ffmpeg: Update to 5.1.2

[lazka]

DLL rdeps:

mingw-w64-aubio
mingw-w64-audaspace
mingw-w64-blender
mingw-w64-ffms2
mingw-w64-freerdp
mingw-w64-gegl
mingw-w64-gr
mingw-w64-gst-libav
mingw-w64-mlt
mingw-w64-mpv
mingw-w64-mtn
mingw-w64-opencascade
mingw-w64-opencv
mingw-w64-openimageio
mingw-w64-OpenSceneGraph
mingw-w64-python-xpra
mingw-w64-qt6-multimedia
mingw-w64-scrcpy
mingw-w64-vlc
mingw-w64-vtk
mingw-w64-wxsvg
mingw-w64-x264

The following depend on it, but don't seem to link, needs investigation:

• mingw-w64-ffmpeg-python -> calls the cli
• mingw-w64-gtk4 -> 6e3c569
• mingw-w64-kfilemetadata-qt5 -> cmake code fails to find ffmpeg as is.. not sure
• mingw-w64-manim _> cli
• mingw-w64-python-pydub _> cli
• mingw-w64-shotcut -> unclear, it looks mostly indirectly and also the cli
• mingw-w64-streamlink -> cli
• mingw-w64-youtube-dl -> cli

According to #10725 (comment) these need 4.4:

• blender -> blender: build with ffmpeg4.4 #15834
• opencascade -> opencascade: build against ffmpeg 4.4 #15835
• OpenSceneGraph -> openscenegraph: build with ffmpeg 4.4 #15847