Update Convex example to convex@0.12.0

[ianmacartney]

Updates Convex to 0.12.0

Improving Documentation or adding/fixing Examples

• The "examples guidelines" are followed from our contributing doc https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md
• Make sure the linting passes by running pnpm build && pnpm lint. See https://github.com/vercel/next.js/blob/canary/contributing/repository/linting.md

[ianmacartney]

pnpm build for me doesn't work, even on vercel's canary branch. It seems caught up by different react type versions:
e.g.

next:build: > next@13.2.5-canary.4 types /Users/ianmacartney/src/next-examples/packages/next
next:build: > tsc --declaration --emitDeclarationOnly --stripInternal --declarationDir dist
next:build: 
next:build: ../../node_modules/.pnpm/@types+react@16.9.17/node_modules/@types/react/index.d.ts(2883,19): error TS2320: Interface 'ElementClass' cannot simultaneously extend types 'Component<any, {}, any>' and 'Component<any, {}, any>'.
...
next:build: ../../node_modules/.pnpm/@types+react@18.0.28/node_modules/@types/react/index.d.ts(3305,13): error TS2717: Subsequent property declarations must have the same type.  Property 'line' must be of type 'SVGProps<SVGLineElement>', but here has type 'SVGProps<SVGLineElement>'.
...
next:build: src/server/render.tsx(219,11): error TS2786: 'App' cannot be used as a JSX component.
next:build:   Its element type 'ReactElement<any, string | JSXElementConstructor<any>> | Component<AppPropsType<any, {}>, any, any> | null' is not a valid JSX element.
next:build:     Type 'Component<AppPropsType<any, {}>, any, any>' is not assignable to type 'Element | ElementClass | null'.
next:build:       Type 'Component<AppPropsType<any, {}>, any, any>' is not assignable to type 'ElementClass'.
next:build:         The types returned by 'render()' are incompatible between these types.
next:build:           Type 'React.ReactNode' is not assignable to type 'import("/Users/ianmacartney/src/next-examples/node_modules/.pnpm/@types+react@18.0.28/node_modules/@types/react/index").ReactNode'.

When I copy my example to a new repo, it works just fine though. It just doesn't have the lint rules there.
Let me know what I can try to get pnpm build working

[ianmacartney]

Running pnpm lint also fails on canary, before my change:

@next/font:typescript: 
Checking formatting...
/Users/ianmacartney/src/next-examples/node_modules/.pnpm/alex@9.1.0/node_modules/alex/cli.js:12
var mdx = require('remark-mdx')
          ^

Error [ERR_REQUIRE_ESM]: require() of ES Module /Users/ianmacartney/src/next-examples/node_modules/.pnpm/remark-mdx@2.3.0/node_modules/remark-mdx/index.js from /Users/ianmacartney/src/next-examples/node_modules/.pnpm/alex@9.1.0/node_modules/alex/cli.js not supported.

[ianmacartney]

pnpm dev works but running pnpm types hits the same issues as build

[ianmacartney]

@leerob could we get a review on this sometime soon? Thanks!