JPEG XL Extra Channel Correlation

[jonnyawsom3]

Feature description

I was on the JXL Discord server helping with #11095, when in the process I realised modular_nb_prev_channels isn't an exposed option. It trades encode/decode speed to reuse similar MA trees from previous channels (Keeping it simple).
At effort 2 with 1 previous channel it gives 12% smaller filesize at 16% slower decoding for a 21 channel multispectral image. I'll try and get results for higher settings soon.