Add Next.js app dir examples and fix some typing #1423

Job	Run time
Lint	43s
Local API diff	29s
Create examples test matrix	7s
Package	39s
Runtime (14)	1m 29s
Runtime (16)	1m 27s
Types (latest)	43s
Runtime (18)	3m 35s
Types (next)	37s
Runtime (20)	1m 33s
Types (beta)	1m 0s
Types (~5.2.0)	43s
Types (~5.1.0)	49s
Types (~5.0.0)	37s
Types (~4.9.0)	41s
Types (~4.8.0)	45s
Types (~4.7.0)	37s
Test examples (framework-nextjs-app-router)	9m 37s
Test examples (framework-nuxt)	2m 10s
Test examples (framework-remix)	2m 6s
Test examples (framework-fastify)	1m 48s
Test examples (framework-nextjs-pages-router)	2m 11s
	34m 26s

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