Create a @styled-system/styled wrapper

[JakeElder]

It would be useful if we could wrap our styled implementation of choice so that it wasn't necessary to use @styled-system/css to resolve styled-system values.

IE, instead of

import styled from '@emotion/styled';
import css from '@styled-system/css';

const Heading = styled("h1")(css({ color: 'brand.1' }));

we could write

import styled from '@styled-system/styled';
const Heading = styled("h1")({ color: 'brand.1' });

or, ideally,

import styled from '@styled-system/styled';
const Heading = styled.h1`color: brand.1`

Presumably this would require some initial setup to in order to be able to support styled-components and @emotion/styled

// your-apps-entry-point.js
import { setStyledImplementation } from '@styled-system/styled';
import styled from '@emotion/styled';
setStyledImplementation(styled);