Webpack 5 supports a single runtimechunk for the Node.js compilation, this solves sharing modules between entrypoints.

Fixes #14632
Fixes #14690

Simplifies on-demand-entries a bit.

Test case for https://github.com/GoogleChromeLabs/native-url/pull/28

Fix https://github.com/vercel/next.js/issues/14419

This addresses the problem of the optimizer postinstall hook causing
delayed installs if run behind a proxy. See https://github.com/ampproject/amp-toolbox/issues/832

Fixes #14070

Most notable new feature: automated hero image preloading.

Release notes: https://github.com/ampproject/amp-toolbox/releases/tag/v2.5.1

Prepares for the upgrade to webpack 5

This removes `fork-ts-checker-webpack-plugin` and instead directly calls the TypeScript API.

This is approximately 10x faster.

Base build: 7s (no TypeScript features enabled)

- `fork-ts-checker-webpack-plugin@3.1.1`: 90s, computer sounds like an airplane
- `fork-ts-checker-webpack-plugin@4.1.6`: 84s, computer did **not** sound like an airplane
- `fork-ts-checker-webpack-plugin@5.0.0-alpha.14`: 90s, regressed
- `npx tsc -p tsconfig.json --noEmit`: 12s (time: `18.57s user 0.97s system 169% cpu 11.525 total`)
- **This PR**: 22s, expected to get better when we run this as a side-car

All of these tests were run 3 times and repeat-accurate within +/- 0.5s.