Deprecate usage of importKind at rule level in favor of using it in selectors #393
Description
Move the importKind option from the rule level to the selector level (as kind), making it more expressive and allowing different values per selector. Add deprecation warnings for the old approach.
Note
It is already supported in the @boundaries/elements package, so it may require only to support it in the rules schema, and add the deprecation warning.
From RFC #370