[v34] JXL lossless

[Kadet]

I noticed that converting jpg to jxl makes the files larger. This means that the lossless transcoding jpg files feature is not used. Transcoding should result in files that are about 20% smaller. I think this option should be used.
And if someone wants plain jxl encoding, they can always create an intermediate png file.

[xnview]

currently jpegxl transcoding is not supported