[css-anchor-position] Rename anchor-default to position-anchor #10004
Description
As the spec has sprouted more properties, a nice naming division has developed - all the props applying to the positioned element start with position-*, while the ones applying to the anchor element start with anchor-*. The obvious exception to this scheme is anchor-default, which is set on the positioned element. The Apple exploration renamed anchor-default to position-anchor, which is a pretty reasonable name.
This also opens up the possibility of using position to shorthand the positioning scheme (position-type: static | relative | etc) and the default anchor (position-anchor: --foo), as the Apple exploration suggested.