Add JPEG XL import support

JPEG XL is an image format that allows for lossy and lossless compression, and is generally better than JPEG at this. LibreOffice currently supports many image file formats, but JPEG XL is not one of them. This project would add such support. The potential for storage savings that support for this image format would bring will mean a better experience for experienced and newer LibreOffice users alike. In addition, web browsers are increasingly supporting JPEG XL (it is available in nightly Firefox builds), so this project will also help LibreOffice users by improving compatibility.