backport: esm externals

[lubieowoce]

• #65041
  • NOTE: needed to change bundlePagesRouterDependencies back to experimental.bundlePagesExternals
• #65519
• #66286
• #66727
• #66990
  • NOTE: It's different the second time. why did nextFlightLoader stuff change?

[github-actions[bot]]

Hi there :wave:

It looks like this PR introduces broken links to the docs, please take a moment to fix them before merging:

Broken link	Type	File
/docs/app/building-your-application/optimizing/package-bundling#analyzing-javascript-bundles	link	/docs/02-app/01-building-your-application/06-optimizing/13-memory-usage.mdx

Thank you :pray:

[ijjk]

Tests Passed

[lubieowoce]

I don't know what's going on, but locally, app-external.test.ts is failing in a completely different way -- EVERYTHING is broken, not just those three tests. it also fails on https://github.com/vercel/next.js/pull/69189, but not in CI.