Enable preservation of heading formatting in GraphQL responses

[StephenBarlow]

Many Markdown headings in our documentation selectively use codefont, such as:

The doStuff function

This formatting is stripped in the value strings returned by a query such as this:

query GetHeadingsForFile {
  file(id: {eq: "abc123"}) {
    name
    childMdx {
      headings {
        value
      }
    }
  }
}

It'd be awesome if the headings or value field accepted an optional raw argument or similar, such that the heading string could be returned as originally written.

Thanks for reading!