chore: Add defaultAs argument to toggleStyledComponent utility

[jonrohan]

This adds a defaultAs argument to the toggleStyledComponent utility. This is because we were defaulting the BaseComponent to 'div' when no as prop was provided. This was incorrect sometimes because the styled component was using something like styled.a

Rollout strategy

• [ ] Patch release
• [ ] Minor release
• [ ] Major release; if selected, include a written rollout or migration plan
• [x] None; if selected, include a brief description as to why

Merge checklist

• [ ] Added/updated tests
• [ ] Added/updated documentation
• [ ] Added/updated previews (Storybook)
• [ ] Changes are SSR compatible
• [ ] Tested in Chrome
• [ ] Tested in Firefox
• [ ] Tested in Safari
• [ ] Tested in Edge
• [ ] (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)