Add Typescript compilation

[timneutkens]

Fixes #7111

• Compile .ts and .tsx files using @babel/preset-typescript
• Doesn't do type checking yet
• Adds tests for functioning HMR and rendering

[github-actions]

Stats from current PR

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	zeit/next.js canary	timneutkens/next.js add/ts	Change
Build Duration	12.2s	12.1s	-118ms
node_modules Size	39.8 MB	39.8 MB	⚠️ +26.8 kB
Total Bundle (main, webpack, commons) Size	207 kB	207 kB	✓
Total Bundle (main, webpack, commons) gzip Size	68.2 kB	68.2 kB	✓
Client _app Size	2.2 kB	2.2 kB	✓
Client _app gzip Size	942 B	942 B	✓
Client _error Size	14.2 kB	14.2 kB	✓
Client _error gzip Size	5.41 kB	5.41 kB	✓
Client pages/index Size	298 B	298 B	✓
Client pages/index gzip Size	235 B	235 B	✓
Client pages/link Size	3.59 kB	3.59 kB	✓
Client pages/link gzip Size	1.62 kB	1.62 kB	✓
Client pages/routerDirect Size	426 B	426 B	✓
Client pages/routerDirect gzip Size	304 B	304 B	✓
Client pages/withRouter Size	408 B	408 B	✓
Client pages/withRouter gzip Size	293 B	293 B	✓
Client main Size	28 kB	28 kB	✓
Client main gzip Size	9.66 kB	9.66 kB	✓
Client commons Size	177 kB	177 kB	✓
Client commons gzip Size	57.3 kB	57.3 kB	✓
Client webpack Size	1.49 kB	1.49 kB	✓
Client webpack gzip Size	774 B	774 B	✓
Base Rendered Size	1.34 kB	1.34 kB	✓
Build Dir Size	616 kB	616 kB	✓

Click to expand serverless stats

	zeit/next.js canary	timneutkens/next.js add/ts	Change
Build Duration	14s	14.6s	⚠️ +606ms
node_modules Size	39.8 MB	39.8 MB	⚠️ +26.8 kB
Total Bundle (main, webpack, commons) Size	207 kB	207 kB	✓
Total Bundle (main, webpack, commons) gzip Size	68.2 kB	68.2 kB	✓
Client _app Size	2.2 kB	2.2 kB	✓
Client _app gzip Size	942 B	942 B	✓
Client _error Size	14.2 kB	14.2 kB	✓
Client _error gzip Size	5.41 kB	5.41 kB	✓
Client pages/index Size	298 B	298 B	✓
Client pages/index gzip Size	235 B	235 B	✓
Client pages/link Size	3.59 kB	3.59 kB	✓
Client pages/link gzip Size	1.62 kB	1.62 kB	✓
Client pages/routerDirect Size	426 B	426 B	✓
Client pages/routerDirect gzip Size	304 B	304 B	✓
Client pages/withRouter Size	408 B	408 B	✓
Client pages/withRouter gzip Size	293 B	293 B	✓
Client main Size	28 kB	28 kB	✓
Client main gzip Size	9.66 kB	9.66 kB	✓
Client commons Size	177 kB	177 kB	✓
Client commons gzip Size	57.3 kB	57.3 kB	✓
Client webpack Size	1.49 kB	1.49 kB	✓
Client webpack gzip Size	774 B	774 B	✓
Serverless pages/link Size	326 kB	326 kB	✓
Serverless pages/link gzip Size	87.2 kB	87.2 kB	-1 B
Serverless pages/index Size	320 kB	320 kB	✓
Serverless pages/index gzip Size	85.3 kB	85.3 kB	-2 B
Serverless pages/_error Size	321 kB	321 kB	✓
Serverless pages/_error gzip Size	85 kB	85 kB	-1 B
Serverless pages/routerDirect Size	320 kB	320 kB	✓
Serverless pages/routerDirect gzip Size	85.4 kB	85.4 kB	-3 B
Serverless pages/withRouter Size	320 kB	320 kB	✓
Serverless pages/withRouter gzip Size	85.4 kB	85.4 kB	-2 B
Build Dir Size	2.19 MB	2.19 MB	✓