[css-gaps-1] Definition of <rule-list> duplicates that in css-syntax-3

[tidoust]

The gap- prefix was dropped from shorthand names. It was also dropped from production rules that these properties use. Unfortunately, that means that the value of column-rule and row-rule now references a <rule-list> production defined in the spec, but that is already defined in css-syntax-3. These value definitions share the same namespace. The prefix is needed there to disambiguate.

[kbabbitt]

Thanks for flagging, this should be fixed in commit 3845f40.