Fix various false positives/negatives after `@property` spec changes

Demo

This is intended to be a tracking issue with more detailed and specific issues to be filed for individual problems.

https://drafts.css-houdini.org/css-properties-values-api/#at-property-rule

These changes where made to the spec or resolved to be made:

• the prelude now allows a list of property names
• descriptors are now optional
• the syntax descriptor now also accepts <syntax> instead of only <string>

I don't currently have a lot of time, but still wanted to give a heads-up for these additions as I think some of the planned updates build on @property?