This setting is an incremental path to the next Flow version enforcing
type annotations on most functions (except some inline callbacks).
Used
```
node_modules/.bin/flow codemod annotate-functions-and-classes --write .
```
to add a majority of the types with some hand cleanup when for large
inferred objects that should just be `Fiber` or weird constructs
including `any`.
Suppressed the remaining issues.
Builds on #25918
Made a couple of fixes to the `devtools-test-shell`
* test selectors aren't available in > React v18.0 either, so we'll need to mock the test selector functions there as well
* `react-dom/client` should map to `react-dom/client` and not `react-dom`
This PR adds an e2e regression app to the react-devtools-shell package. This app:
* Has an app.js and an appLegacy.js entrypoint because apps prior to React 18 need to use ReactDOM.render. These files will create and render multiple test apps (though they currently only render the List)
* Moved the ListApp out of the e2e folder and into an e2e-apps folder so that both e2e and e2e-regression can use the same test apps
* Creates a ListAppLegacy app because prior to React 16.8 hooks didn't exist.
* Added a devtools file for the e2e-regression
* Modifies the webpack config so that the e2e-regression React app can use different a different React version than DevTools
Jan Kassens
Luna Ruan