Stop putting react-app-env.d.ts in src

Created by: devuxer

(This pertains to CRA w/ the --typescript flag.)

Putting a loose d.ts file at the top level of src adds clutter and breaks the convention of putting all d.ts files together in a folder, such as "types".

Suggestions to remedy this (in order of preference):

1. Honor the new location of react-app-env.d.ts if we move it.
2. Allow us to configure where this file goes.
3. Place the file in src/types.

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EDIT:

@nhooyr Given its confusing, you could also add a comment to the generated file explaining why its there.

@bugzpodder This file was created to include create-react-app specific types. Removing it will cause errors like:

TypeScript error in ~/src/App.tsx(2,18):
Cannot find module './logo.svg'.  TS2307

    1 | import React from 'react';
  > 2 | import logo from './logo.svg';
      |                  ^
    3 | import './App.css';
    4 | 
    5 | const App: React.FC = () => {

This was created from #5611 if you want more details.