Revert "Revert "Force resolution to use vendored React""
This reverts commit 4e7709272fa8fbe162f76ec7395d4c15a50eacc1.
We do need it since `next build` just requires `next`.
Every require we do needs to use the vendored React.
We can't rely on bundlers here since `next build` uses default Node.js module resolution.
