Add support for DNG 1.7

[qdwang]

DNG 1.7 supports JPEG XL content which is very useful for dng compression.

I can provide two samples here:

samples.zip

One is in Bayer pattern, the other is in linearRGB pattern. Both of them can be correctly opened by Lightroom latest version and MacOS Preview.

If you guys need more samples, I created a website TinyDNG which can compress any DNG files to a JPEG XL compressed DNG.