Playground support for uncontrolled components

[epicfaace]

Description

We've had issues like #1316 and #1394 that are hard to reproduce on the playground because they only happen for uncontrolled components. The playground, on the other hand, has a controlled component, so we can't catch these errors.

Solution

Add a checkbox called "controlled component" in the playground. By default, it should be checked.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Please leave a comment if this is still an issue for you. Thank you.