fix(v2): add @babel/preset-typescript to babel-loader

[deniaz]

Motivation

With #2221 docusaurus v2 is able to detect {ts,tsx} pages and components, but as soon as babel hits TypeScript syntax it fails. While the docusaurus babel.config.js includes @babel/preset-typescript, babel-loader inside the Webpack config does not.

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

1. Add typescript.tsx to your pages directory
2. Add TypeScript syntax

import React from 'react';

export default () => {
  let name: string = 'World';

  return (
    <h1>Hello {name}!</h1>
  );
};

3. Run docusaurus
4. Check localhost:3000/typescript

Related PRs

#2221

[docusaurus-bot]

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[yangshun]

Thank you!