Resolves #8827

Page 40 of https://www.color.org/icc32.pdf

This tag specifies the media white point and is used for generating absolute colorimetry.

This is mostly a copy of https://pillow.readthedocs.io/en/stable/reference/ImageCms.html#PIL.ImageCms.core.CmsProfile.media_black_point, although without

This tag was available in ICC 3.2, but it is removed from version 4.

Looking for evidence that media black point was removed in version 4, I found https://www.color.org/v4spec.xalter, that mentions the black tag, but not the white tag. Checking in https://www.color.org/specification/icc1v43_2010-12.pdf, the black tag is gone, but the white tag is still present.