Fix `pnpm build --filter next` on a clean repository (#68693)
`next` uses `@next/font` during type emission (referenced in
`packages/next/types/$$compiled.internal.d.ts`). However, we currently
don't build `@next/font` before `next` since it's not declared
dependency.
Added to `devDependencies` since that's what `@next/font` is to `next`.
In prod, we use the vendored version.
