FFmpegKit Flutter v6.0.0

• Based on FFmpegKit native v6.0 releases
• Includes FFmpeg v6.0
• API Changes
  • Improves Statistics.getTime() method to return milliseconds as double
  • Drops custom fd protocol on Android. ffmpeg 6.0 has a new built-in fd protocol that can be used instead
  • FFmpegKit binaries built without bitcode on iOS and tvOS platforms
• Uses the new versions of cpu_features, dav1d, expat, fontconfig, freetype, fribidi, giflib, gmp, gnutls, harfbuzz, libjpeg-turbo, kvazaar, leptonica, libaom, libass, libiconv, libilbc, libpng, libsndfile, libvidstab, libvpx, libwebp, libxml2, openssl, opus, srt, tesseract, x264 and zimg
• Fixes #599

Tested using v6.0.0 test applications