feat(rlottie) add LVGL-Rlottie interface as 3rd party lib (#2700)

docs/libs/index.md

@@ -17,5 +17,6 @@
    gif
    freetype
    qrcode
+   rlottie
 ```
 

docs/libs/rlottie.md

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+```eval_rst
+.. include:: /header.rst
+:github_url: |github_link_base|/libs/rlottie.md
+```
+
+
+# Lottie player
+Allows to use Lottie animations in LVGL. Taken from this [base repository](https://github.com/ValentiWorkLearning/lv_rlottie)
+
+LVGL provides the interface to [Samsung/rlottie](https://github.com/Samsung/rlottie) library's C API. That is the actual Lottie player is not part of LVGL, it needs to be built separately.
+
+## Build Rlottie
+To build Samsung's Rlottie C++14-compatible compiler and optionally CMake 3.14 or higher is required.
+
+To build on desktop you can follow the instrutions from Rlottie's [README](https://github.com/Samsung/rlottie/blob/master/README.md). In the most basic case it looks like this:
+```
+mkdir rlottie_workdir
+cd rlottie_workdir
+git clone https://github.com/Samsung/rlottie.git
+mkdir build >
+cd build
+cmake ../rlottie
+make -j
+make install
+```
+
+And finally add the `-lrlottie` flag to your linker.
+
+On embedded systems you need to take care of integrating Rlottie to the given build system.
+
+
+## Usage
+
+You can use animation from files or raw data (text). In either case first you need to enable `LV_USE_RLOTTIE` in `lv_conf.h`.
+
+
+The `width` and `height` of the object be set in the *create* function and the animation will be scaled accordingly.
+
+### Use Rlottie from file
+
+To create a Lottie animation from file use:
+```c
+  lv_obj_t * lottie = lv_rlottie_create_from_file(parent, width, height, "path/to/lottie.json");
+```
+
+Note that, Rlottie uses the standard STDIO C file API, so you can use the path "normally" and no LVGL specific driver letter is required.
+
+
+### Use Rlottie from raw string data
+
+`lv_example_rlottie_approve.c` contains an example animation in raw format. Instead storing the JSON string a hex array is stored for the following reasons:
+- avoid escaping `"` in the JSON file
+- some compilers don't support very long strings
+
+`lvgl/scripts/filetohex.py` can be used to convert a Lottie file a hex array. E.g.:
+```
+./filetohex.py path/to/lottie.json > out.txt
+```
+
+To create an animation from raw data:
+
+```c
+extern const uint8_t lottie_data[];
+lv_obj_t* lottie = lv_rlottie_create_from_raw(parent, width, height, (const char *)lottie_data);
+```
+
+## Getting animations
+
+Lottie is standard and popular format so you can find many animation files on the web.
+For example: https://lottiefiles.com/
+
+You can also create your own animations with Adobe After Effects or similar software.
+
+## Example
+```eval_rst
+
+.. include:: ../../examples/libs/rlottie/index.rst
+
+```
+
+## API
+
+```eval_rst
+
+.. doxygenfile:: lv_rlottie.h
+  :project: lvgl