[css-logical] Define mask-image-transform and mask-border-image-transform

[dirkschulze]

CSS Logical 1 should probably define mask-image-transform and mask-border-image-transform respectively to background-image-transform and border-image-transform.

[LeaVerou]

Should we close this? I can't find any current reference to any *-image-transform properties, and it seems the use cases for such a thing would be covered by @image (which the WG has resolved to add to images-5).