Bug: Server hydration mistmatch and radio group with defaultChecked

<!-- Please provide a clear and concise description of what the bug is. Include screenshots if needed. Please test using the latest version of the relevant React packages to make sure your issue has not already been fixed. --> When hydrating from the server, whenever there's a mismatch in the initially checked input in a radio button group and the inputs use `defaultChecked` (uncontrolled), there is no warning of that mismatch and the component behaves in a buggy way for the input that was initially selected in the server payload (the `onChange` callback prop is not fired for the input that was marked as selected in the initial html, when selecting it). Worth noting that using a controlled input (using `checked`) makes the bug go away. React version: 16.13.1 ## Steps To Reproduce 1. In the example provided below, make sure you refresh the browser within Code Sandbox. 2. Check the first radio button. Verify that the radio is checked, but the text next to it still shows as "not checked" (which means the onChange prop was not triggered) 3. Attempt to select any other option (works fine), and then back the first one (works fine too). 4. Refreshing the page again, choosing any other option other than the first works fine. <!-- Your bug will get fixed much faster if we can run your code and it doesn't have dependencies other than React. Issues without reproduction steps or code examples may be immediately closed as not actionable. --> Link to code example: https://codesandbox.io/s/affectionate-stonebraker-3wj68 <!-- Please provide a CodeSandbox (https://codesandbox.io/s/new), a link to a repository on GitHub, or provide a minimal code example that reproduces the problem. You may provide a screenshot of the application if you think it is relevant to your bug report. Here are some tips for providing a minimal example: https://stackoverflow.com/help/mcve. --> ## The current behavior I know that using hydrate doesn't guarantee fixing the mismatches, but …