feat!: no-unknown-at-rules -> no-invalid-at-rules

[nzakas]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request?

Renamed no-unknown-at-rules to no-invalid-at-rules to cover more cases.

What changes did you make? (Give an overview)

• Renamed source files from no-unknown-at-rules.* to no-invalid-at-rules.*
• Added checks for invalid preludes, unknown descriptors, and invalid descriptor values.
• Added more tests
• Updated docs

Related Issues

Is there anything you'd like reviewers to focus on?

There are type errors that will be resolved once #11 is merged and I can rebase on top of it.

[jeddy3]

Looks ace!

Can I ask if the ambition is to integrate more specific validity cases (not caught by csstree) into this rule or add separate rules for those?

For example, @property requires some descriptors:

@property rules require a syntax and inherits descriptor; if either are missing, the entire rule is invalid and must be ignored. The initial-value descriptor is optional only if the syntax is the universal syntax definition, otherwise the descriptor is required; if it’s missing, the entire rule is invalid and must be ignored.

It'd catch an easy mistake for people to make.

[nzakas]

@jeddy3

Can I ask if the ambition is to integrate more specific validity cases (not caught by csstree) into this rule or add separate rules for those?

I honestly haven't thought that far ahead yet. 😄 I could imagine wanting that check in this rule, but I'm not 100% sure yet. I'd like to just start with what csstree is providing for the first version and then think about things a bit more once we've got some feedback.

[mdjermanovic]

There are merge conflicts now. Also, some tests were failing.