Revive: dumping/ffmpeg_backend: Various fixes (#6528)

* dumping/ffmpeg_backend: Add FPS filter

So that the recorded video can be at 60FPS (which is supported by most encoders) while still maintaining correct speed.

* dumping/ffmpeg_backend: Add HW context support

Required for some HW acceled encoders. Not tested as my devices don't seem to require this.

* CMake: Copy avfilter dll for MSVC

* CMakeLists: Require FFmpeg 4.0

* ffmpeg: Fix dumper compile error on MSVC.

* ffmpeg: Address review comments.

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Co-authored-by: zhupengfei <zhupf321@gmail.com>

CMakeModules/CopyCitraFFmpegDeps.cmake

@@ -3,8 +3,10 @@ function(copy_citra_FFmpeg_deps target_dir)
     set(DLL_DEST "${CMAKE_BINARY_DIR}/bin/$<CONFIG>/")
     windows_copy_files(${target_dir} ${FFMPEG_DIR}/bin ${DLL_DEST}
         avcodec*.dll
+        avfilter*.dll
         avformat*.dll
         avutil*.dll
+        postproc*.dll
         swresample*.dll
         swscale*.dll
     )