feat: Support for getLayout in generated _app.tsx

[AndKenneth]

Is your feature request related to a problem? Please describe.

Hi Yall. I've been trying to implement layouts on my T3 app and I've run into some issues integrating it with the way next recommends in their documentation.

https://nextjs.org/docs/basic-features/layouts

I've tried integrating this with my app, and while I can get it working in isolation, the particularities of the custom types involved gets very complex very quickly, and generally falls apart when I try and reintegrate trpc and nextauth as set up in ct3a.

Overall this is a fairly painful and frustrating experience for less experienced typescript developers that requires understanding what the types are doing here to solve.

Describe the solution you'd like to see

I'd propose that the generated _app.tsx file in ct3a supports exported pages including a getLayout function, and wraps the component in the layout per the Next.JS docs.

Describe alternate solutions

We could wait for app router to be fully supported which has a much more powerful and sane layout system. Julius recommended this approach in another issue.

I would argue that if someone who knows what they're doing could take a look at this, it could be a quick job, and would save newer developers a lot of pain. Maybe someone knows better than me that app router is coming soon so it's not worth it, but the linked issue is more than 6 months ago and I see a few recent bumps asking for a solution.

[Rykuno]

type NextPageWithLayout = NextPage & {
  getLayout?: (page: React.ReactElement) => React.ReactNode;
};

type AppPropsWithLayout = AppType & {
  Component: NextPageWithLayout;
  pageProps: { session: Session | null };
};

const MyApp = ({
  Component,
  pageProps: { session, ...pageProps }
}: AppPropsWithLayout) => {
  const getLayout = Component.getLayout ?? (page => page);

....

[juliusmarminge]

Rykuno's code looks about right. We have this in some of tRPC's examples but I don't think we're really using them post-setup 😓

[juliusmarminge]

Closing this as we're getting closer to the app dir option and I don't think we want to make this change for pages