Add `.d.ts` to Jest's moduleFileExtensions

Created by: ViieeS

Without it test fails when you try to import .d.ts modules using shorten form (eg. import {TODO_ANY} from 'src/react-app-env';)

Reproduction:

1. Create basic TypeScript CRA app
2. Add import './react-app-env' to src/App.tsx.
3. npm run test

Error:

> react-ts-app@0.1.0 test /react-ts-app
> react-scripts test
 FAIL  src/App.test.tsx
  ● Test suite failed to run

    Cannot find module './react-app-env' from 'App.tsx'

    However, Jest was able to find:
        './react-app-env.d.ts'

    You might want to include a file extension in your import, or update your 'moduleFileExtensions', which is currently ['web.js', 'js', 'web.ts', 'ts', 'web.tsx', 'tsx', 'json', 'web.jsx', 'jsx', 'node'].

    See https://jestjs.io/docs/en/configuration#modulefileextensions-array-string

    However, Jest was able to find:
        './App.css'
        './App.test.tsx'
        './App.tsx'

    You might want to include a file extension in your import, or update your 'moduleFileExtensions', which is currently ['web.js', 'js', 'web.ts', 'ts', 'web.tsx', 'tsx', 'json', 'web.jsx', 'jsx', 'node'].