Currently, global name-defining at-rules, like @font-face, are allowed inside of "contextually conditional" rules like @container or @scope (which depend on tree information to resolve), and we just ignore the conditional-ness and define them unconditionally, instead. This came up again for @mixin.

We want to be consistent across these similar rules, as much as possible. Is the current behavior (which wasn't intentionally designed, it's just what implementations happened to do) what we want to continue with? Or do we want to try and change things so that using these at-rules inside of contextual conditionals is invalid?