core/dumping: Add FFmpeg implementation

Sorry for the large diff, the implementation is quite long, and I can't really find a good way to split it into commits.

src/core/CMakeLists.txt

@@ -446,6 +446,13 @@ add_library(core STATIC
     tracer/recorder.h
 )
 
+if (ENABLE_FFMPEG)
+    target_sources(core PRIVATE
+        dumping/ffmpeg_backend.cpp
+        dumping/ffmpeg_backend.h
+    )
+endif()
+
 create_target_directory_groups(core)
 
 target_link_libraries(core PUBLIC common PRIVATE audio_core network video_core)
@@ -464,3 +471,7 @@ if (ARCHITECTURE_x86_64)
     )
     target_link_libraries(core PRIVATE dynarmic)
 endif()
+
+if (ENABLE_FFMPEG)
+    target_link_libraries(core PRIVATE FFmpeg::avcodec FFmpeg::avformat FFmpeg::swscale FFmpeg::swresample FFmpeg::avutil)
+endif()