[css-anchor-position] position-anchor should be defined as a longhand of position #10321
Description
In #10004 we proposed to rename anchor-default to position-anchor and to allow position to shorthand both arguments.
The resolution was taken to rename the property, but because people were unsure about how to define a combined syntax with position-container, a combined shorthand syntax for the two was deferred.
However the question of whether position resets position-anchor was not resolved, not edited in, and not put on the agenda for follow-up as agreed by the CSSWG.
If we are to create a shorthand syntax in the future, we need the resetting relationships to be resolved and implemented now, i.e. position needs to reset position-anchor even if it can't set it to anything but the initial value.