feat(lib) add ffmpeg video and image decoder (#2805)

* add ffmpeg decoder to extra/libs

* fix(Kconfig) add ffmpeg configuration

Signed-off-by: pengyiqiang <pengyiqiang@xiaomi.com>

* feat(example) add ffmpeg decoder example

Signed-off-by: pengyiqiang <pengyiqiang@xiaomi.com>

* update lv_conf_template.h

* feat(example) add picture and video to ffmpeg example

* docs(libs) update FFMpeg introduction

Signed-off-by: pengyiqiang <pengyiqiang@xiaomi.com>

* fix(ffmpeg) replace with new videos and examples

Signed-off-by: pengyiqiang <pengyiqiang@xiaomi.com>

* fix(ffmpeg) remove the include of lv_img_cache.h

* fix(ffmpeg) add LV_ASSERT_OBJ

* Update examples/libs/ffmpeg/lv_example_ffmpeg_2.c

Co-authored-by: pengyiqiang <pengyiqiang@xiaomi.com>
Co-authored-by: Gabor Kiss-Vamosi <kisvegabor@gmail.com>

docs/libs/ffmpeg.md

@@ -0,0 +1,34 @@
+```eval_rst
+.. include:: /header.rst 
+:github_url: |github_link_base|/libs/ffmpeg.md
+```
+
+# FFmpeg support
+[FFmpeg](https://www.ffmpeg.org/) A complete, cross-platform solution to record, convert and stream audio and video.
+
+## Install FFmpeg
+- Download FFmpeg from [here](https://www.ffmpeg.org/download.html)
+- `./configure --disable-all --disable-autodetect --disable-podpages --disable-asm --enable-avcodec --enable-avformat --enable-decoders --enable-encoders --enable-demuxers --enable-parsers --enable-protocol='file' --enable-swscale --enable-zlib`
+- `make`
+- `sudo make install`
+
+## Add FFmpeg to your project
+- Add library: `FFmpeg` (for GCC: `-lavformat -lavcodec -lavutil -lswscale -lm -lz -lpthread`)
+
+## Usage
+
+Enable `LV_USE_FFMPEG` in `lv_conf.h`.
+
+See the examples below.
+
+Note that, the FFmpeg extension doesn't use LVGL's file system. 
+You can simply pass the path to the font as usual on your operating system or platform.
+
+## API
+
+```eval_rst
+
+.. doxygenfile:: lv_ffmpeg.h
+  :project: lvgl
+
+```

docs/libs/index.md

@@ -18,5 +18,6 @@
    freetype
    qrcode
    rlottie
+   ffmpeg
 ```