<graphql-query> should take a <script> tag

[bennypowers]

Hey! Thanks for putting this element together, looks great and I'm excited to get cracking with it.

What do you think about making the slot for <graphql-query> take a script element? It would look like this in practise:

  <graphql-query id="query" result="{{starShipsData}}" defer>
    <script type="application/graphql">
      query {
        allStarships(first: 5, filter: {pilots_some: {name_not: ""}}) {
          name
          class
          pilots {
            name
            homeworld {
              name
            }
          }
        }
      }
    </script>
  </graphql-query>

This is how <markdown-element> does things.

Why does this matter?

1. the content actually is of script type application/graphql, so might as well be explicit
2. semantically, screen readers etc will skip over the text content of the query
3. editor tooling could work better inside the script tag (syntax highlighting, etc)

I'm happy to provide a PR