#1209 | allow widget to be wrapped as React.ForwardedRef

[anlesk]

Reasons for making this change

Allow widget to be wrapped by React.ForwardedRef.
This fixes #1209

Checklist

• I'm updating documentation
  • I've checked the rendering of the Markdown text I've added
• I'm adding or updating code
  • I've added and/or updated tests
  • I've updated docs if needed
  • I've run npm run cs-format on my branch to conform my code to prettier coding style
• I'm adding a new feature
  • I've updated the playground with an example use of the feature

[epicfaace]

Thanks!

[epicfaace]

@anlesk would you mind doing the same with getFieldComponent as well? thanks! https://github.com/mozilla-services/react-jsonschema-form/blob/98952b7f2a6add8909a2c7209797f3770d4a04f7/src/components/fields/SchemaField.js#L34