Zeiss CZI: fix value of Rectangle.Y

The stored Y coordinate is the actual Y coordinate; it doesn't need to
be subtracted from the image height.

Fixes ticket #11367.
Zeiss CZI: fix copying of prestitched tiles

This uses the stored tile row/column instead of assuming that tiles were
acquired in comb mode.  It also prevents tiles from being copied to the
wrong row when the image width is greater than the sum of the tile widths.

Fixes #11784.
Zeiss CZI: fix reading of RGB images

The channel count and interleaved values were previously set
incorrectly; openBytes also did not account for the fact that RGB images
are stored in BGR order.

Fixes #11233.