Outstanding syntaxes needing validators

[ben-eb]

• [x] clip-path: <clip-source> | [ <basic-shape> || <geometry-box> ] | none
• [x] grid-auto-columns: <track-size>
• [ ] grid-column-end: <grid-line>
• [ ] grid-template-columns: none | <track-list> | <auto-track-list> | subgrid <line-name-list>?
• [x] mask-image: <mask-reference>#
• [ ] shape-outside: none | <shape-box> || <basic-shape> | <image>
• [ ] transition-property: none | <single-transition-property># (MDN has this as IDENT which I take to mean using isCustomIdent)