feat(libs): add libpng decoder (#4569)

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

docs/libs/index.rst

@@ -11,6 +11,7 @@
     tjpgd
     libjpeg_turbo
     lodepng
+    libpng
     gif
     freetype
     tiny_ttf

docs/libs/libpng.rst

@@ -0,0 +1,42 @@
+==============
+libpng decoder
+==============
+
+libpng is the official PNG reference library. It supports almost all PNG features, is extensible, and has been extensively tested for over 28 years.
+Detailed introduction: `libpng <http://www.libpng.org/pub/png/libpng.html>`__.
+
+Install
+-------
+
+.. code:: bash
+
+    sudo apt install libpng-dev
+
+Add libpng to your project
+--------------------------
+
+.. code:: cmake
+
+    find_package(PNG REQUIRED)
+    include_directories(${PNG_INCLUDE_DIR})
+    target_link_libraries(${PROJECT_NAME} PRIVATE ${PNG_LIBRARIES})
+
+Usage
+-----
+
+Enable :c:macro:`LV_USE_LIBPNG` in ``lv_conf.h``.
+
+See the examples below.
+It should be noted that each image of this decoder needs to consume ``image width x image height x 4`` bytes of RAM, 
+and it needs to be combined with the ref:`image-caching` feature to ensure that the memory usage is within a reasonable range.
+
+Example
+-------
+
+.. include:: ../examples/libs/libpng/index.rst
+
+API
+---
+
+:ref:`libpng`
+