De-duplicate code in twig templates

The code in block--lb-cards--variation-*.html.twig contains highly duplicated code. In order to maintain a DRY codebase and reduce our codebase “weight”, we should de-duplicate code wherever possible.

A possible model for this could be:

• block--lb-cards.html.twig contains the base code for all variants with block statements and switching logic.
• set statements should all be made before any div to maintain separation of concerns.
• block--lb-cards--variation-*.html.twig have set statements to assign variables, then use extends to reference the base template.

Acceptance Criteria

1. code diff should have lots of deletions
2. front-end should have no changes from prior behavior