Add support for function components that return null

[rvetere]

Add support for function components that only return null:

export const DataTableColumnDocs: FunctionComponent<
  IDataTableColumn<object>
> = () => {
  return null;
};

and add support for components that only return a prop (directly, without a fragment):

export const AuthenticatedBoundary = ({
  children,
  fallback,
}: AuthenticatedBoundaryProps) => {
  const { isLoggedIn } = useAuthentication();

  if (!isLoggedIn) {
    return fallback;
  }

  return children;
};

Fixes #926

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[danez]

What worries me is that literaly any function that returns null will be detected as react component.
Same for the other usecase.