* Improve DevTools editing interface
This commit adds the ability to rename or delete keys in the props/state/hooks/context editor and adds tests to cover this functionality. DevTools will degrade gracefully for older versions of React that do not inject the new reconciler rename* or delete* methods.
Specifically, this commit includes the following changes:
* Adds unit tests (for modern and legacy renderers) to cover overriding props, renaming keys, and deleting keys.
* Refactor backend override methods to reduce redundant Bridge/Agent listeners and methods.
* Inject new (DEV-only) methods from reconciler into DevTools to rename and delete paths.
* Refactor 'inspected element' UI components to improve readability.
* Improve auto-size input to better mimic Chrome's Style editor panel. (See this Code Sandbox for a proof of concept.)
It also contains the following code cleanup:
* Additional unit tests have been added for modifying values as well as renaming or deleting paths.
* Four new DEV-only methods have been added to the reconciler to be injected into the DevTools hook: overrideHookStateDeletePath, overrideHookStateRenamePath, overridePropsDeletePath, and overridePropsRenamePath. (DevTools will degrade gracefully for older renderers without these methods.)
* I also took this as an opportunity to refactor some of the existing code in a few places:
* Rather than the backend implementing separate methods for editing props, state, hooks, and context– there are now three methods: deletePath, renamePath, and overrideValueAtPath that accept a type argument to differentiate between props, state, context, or hooks.
* The various UI components for the DevTools frontend have been refactored to remove some unnecessary repetition.
This commit also adds temporary support for override* commands with mismatched backend/frontend versions:
* Add message forwarding for older backend methods (overrideContext, overrideHookState, overrideProps, and overrideState) to the new overrideValueAtPath method. This was done in both the frontend Bridge (for newer frontends passing messages to older embedded backends) and in the backend Agent (for older frontends passing messages to newer backends). We do this because React Native embeds the React DevTools backend, but cannot control which version of the frontend users use.
* Additional unit tests have been added as well to cover the older frontend to newer backend case. Our DevTools test infra does not make it easy to write tests for the other way around.
DevTools previously used the NPM events package for dispatching events. This package has an unfortunate flaw though- if a listener throws during event dispatch, no subsequent listeners are called. I've replaced that event dispatcher with my own implementation that ensures all listeners are called before it re-throws an error.
This commit replaces that event emitter with a custom implementation that calls all listeners before re-throwing an error.
