Add JPEG XR (.jxr) format support for conversion and compression

[cherinyy]

Is your feature request related to a problem? Please describe.
I need to work with JPEG XR (.jxr) files for specific use cases (e.g., HDR imaging, transparency support), but Squoosh currently lacks support for this format. This forces me to use other tools for JXR conversion/compression, which disrupts my workflow and prevents me from leveraging Squoosh's excellent comparison interface for this format.

Describe the solution you'd like

1. Add support for importing/opening .jxr files in Squoosh
2. Add a JPEG XR encoder/compressor to convert images to .jxr format
3. Include compression options specific to JXR (e.g., quality tiers, overlap filtering, color space optimizations)
4. (Optional) Support for advanced JXR features like transparency and HDR

Does other service/app have this feature?

• Microsoft Paint (basic JXR support)
• Adobe Photoshop (via plugin)
• CloudConvert.com (conversion support)
• ImageMagick (CLI conversion)
• Online-Convert.com (JXR conversion)

Additional context

• JPEG XR is standardized as ISO/IEC 29199-2 and supports features like:
  • Lossless and lossy compression
  • Alpha channel transparency
  • HDR/WCG imaging
  • Tile/stripe structure
• Potential implementation paths:
  • Integrate existing open-source libraries like libjpegxr or Microsoft's JXR Library (jxrlib)
  • WASM compilation could be explored for browser compatibility
• Example use case: Compressing medical/industrial images where JXR's lossless compression is preferred
• W3C considered JXR for web images though adoption has been limited