Devtools: Allow editing context

React version: 16.13 and `0.0.0-experimental-aae83a4b9 ## Steps To Reproduce 1. Goto https://codesandbox.io/s/xenodochial-field-rfdjz 2. Try editing value of `MessageListContext.Provider` Link to code example: https://codesandbox.io/s/xenodochial-field-rfdjz ## The current behavior Context from `createContext` can't be edited in the current devtools (provider, consumer, hooks) ## The expected behavior Context value should be editable. I already proposed an implementation for [Provider](https://github.com/facebook/react/pull/18255) and [Consumer](https://github.com/facebook/react/pull/18257).