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>

examples/libs/lv_example_libs.h

@@ -19,6 +19,7 @@ extern "C" {
 #include "freetype/lv_example_freetype.h"
 #include "gif/lv_example_gif.h"
 #include "lodepng/lv_example_lodepng.h"
+#include "libpng/lv_example_libpng.h"
 #include "qrcode/lv_example_qrcode.h"
 #include "rlottie/lv_example_rlottie.h"
 #include "tjpgd/lv_example_tjpgd.h"