Adds support for decoding JPEG XL (image/jxl) images in Blink using jxl-rs, a memory-safe pure Rust decoder. JPEG XL is a modern image format standardized as ISO/IEC 18181 that offers: - Progressive decoding for improved perceived loading performance - Support for wide color gamut, HDR, and high bit depth - Animation support This implementation uses jxl-rs (https://github.com/libjxl/jxl-rs) instead of the C++ libjxl reference decoder to meet Chromium's memory safety requirements. The decoder is gated behind the enable-jxl-image-format flag and enable_jxl_decoder build flag. CL: https://chromium-review.googlesource.com/c/chromium/src/+/7184969