[css-masking-2] Add mask-position-{block|inline} #595
Description
In #103 it was resolved to add the physical longhands mask-position-x and mask-position-y and make mask-position a shorthand of them. (See also #251)
As we like to push logical properties and values and the corresponding background-position-{block|inline} are already defined, the logical versions mask-position-block and mask-position-inline should also be added.
Sebastian