AudioFilter, GreenScreen, WaterMark: bump ffmpeg 6

AudioFilter/FilterAudioSubscriber.cpp

AudioFilter/build.sh

AudioFilter/ffmpeg/package.json

AudioFilter/ffmpeg/rules.mak

AudioFilter/ffmpeg/windows-configure-make.sh

GreenScreen/build.sh

GreenScreen/ffmpeg/package.json

GreenScreen/ffmpeg/rules.mak

WaterMark/build.sh

WaterMark/ffmpeg/package.json

WaterMark/ffmpeg/rules.mak

WaterMark/testPreferences.yml

build-plugin.py

contrib/freetype/package.json

lib/AVFrameIO.h

lib/frameFilter.cpp

lib/mediaStream.h