Warn against missing use of {{ block.shopify_attributes }} in blocks with tag: null #867

Is your feature request related to a problem? Please describe.

“When ”tag”: null set in block schema, then {{ block.shopify_attributes }} must exist in the markup of the template”

Describe the solution you'd like
For block/*.liquid files, when the {% schema %} contains "tag": null at the top level, then we should report a WARNING severity offence on tag: null

Additional context

https://shopify.dev/docs/storefronts/themes/architecture/blocks/theme-blocks/schema#tag:~:text=of%20the%20block.-,Caution,index%20when%20merchants%20re%2Dorder%20blocks%20without%20leaving%20orphaned%20HTML%20elements.,-Copy