Add forward ref to React SVG Component

Created by: GasimGasimzada

This pull request adds "ref" option to SVGR loader; so that, the root svg component ref can be accessed. The way it works is that SVGR creates a forward ref and passed the ref to svg component using svgRef prop.

Example:

import React, { Component } from 'react';
import { ReactComponent as Logo } from './logo.svg'; // CRA default logo file

class App extends Component {
    myRef = React.createRef();

    componentDidMount() {
        console.log(this.myRef);
    }

    render() {
        return (<Logo svgRef={this.myRef} />);
     }
}

This example will print the svg element.

Testing

I have added unit tests to webpack/SVGComponent.js; however, I was not able to perform the test. yarn e2e:docker -- --test-suite kitchensin kept giving me permission denied error inside the container.