Log Message:
SDL2_image: update to 2.6.3.

2.6.2:
 * Updated autotools to use ax_compute_relative_paths, fixing homebrew on macOS

2.6.1:
 * Fixed loading grayscale PNGs when using stb_image

2.6.0:
 * Added support for building with CMake
 * Added stb_image as the default backend for JPG and PNG images loading.
   To use libpng and libjpg instead, configure using --disable-stb-image
 * Added IMG_LoadSizedSVG_RW()
 * Added support for AVIF images (https://github.com/AOMediaCodec/libavif)
 * Added IMG_ReadXPMFromArrayToRGB888()
 * Added support for JXL images (https://jpegxl.info/)
 * Added support for QOI images (https://qoiformat.org/)
 * Fixed XCF regression introduced in 2.0.5
 * Added support for loading animated GIFs
 * LoadBMP() now loads files using SDL2
 * Allow using libwebpdecoder instead libwebp