Pass through properties to top-level MDX component

[rfrowe]

Closes #183 by fixing the props shadowing issue in scope. As was, props inside the mdx scope was being overridden by the implicit empty props passed to the top-level component for the rendered MDX. This extracts props from scope and overrides the props used on construction by wrapping the top-level component.

[hashicorp-cla]

All committers have signed the CLA.