Improve group order for progression
Improve group order for progression

Currently for the progression the first group in  the boundary of the
next square is the center of the left hand side.
After this change we always start with a tile next to a corner, which
yields a nicer progression, with more regular shapes.

libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl