strong-run-of-four-splits

A **** run flanked by real word content on both sides is a closer immediately followed by an opener: two separate Strong nodes, not one nested/empty span

§5.3

Input

**one part text **** other part**

Output AST

- type: Paragraph
  children:
    - type: Strong
      children:
        - type: Text
          value: one part text
    - type: Strong
      children:
        - type: Text
          value: other part