esm: Unflag --experimental-modules

[guybedford]

This PR unflags the --experimental-modules support making modules on-by-default, while remaining backwards-compatible with the current runMain.

This PR should only land after the remaining PRs have been fully considered:

• Fix 3 remaining task_queue timing issues in this PR (discussed in esm: Unflag --experimental-modules #29866 (comment))
• Re-flagging --experimental-json-modules (module: Revert remove experimental status from JSON modules #29754)
• Package-relative loading (module: resolve self-references #29327)
• Unflagging --experimental-exports (esm: unflag --experimental-exports #29867)
• Bootstrap refactoring (Modules bootstrap refactoring #29937)
• Resolution on exports fallback to main (ESM "exports" field disables "main" lookup #29932)
• Conditional exports considerations (module: Conditional exports #29978)
• Matching ESM extensions order (esm: modify resolution order for specifier flag #29974)

In addition to:

• Ensuring documentation has been fully reviewed for an unflagged modules release
• Sign off from the modules group.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

[guybedford]

//cc @nodejs/modules-active-members

[guybedford]

The three failing tests in this PR are:

• ./node ./test/addons/async-hooks-promise/test.js the async hook promise injection is not being removed despite being disabled in https://github.com/nodejs/node/pull/29848/files#diff-e6db408e12db906ead6ddfac3de15a6fR314. @jasnell would value your input on this one if you have any suggestions here.
• ./node ./test/addons/make-callback-recurse/test.js, ./node ./test/node-api/test_make_callback_recurse/test.js both seem due to subtle timing changes with the switch to a promise-based bootstrap.

[Trott]

Adding WIP label based on PR description. Feel free to remove when appropriate, swap out with blocked label, or whatever. No strong opinions here. Just seems like the right thing to me. (The WIP label helps me in my workflow with the repository, so it's not just cosmetic for me, if that matters. But again, no strong opinions on this particular PR in that regard.)

[guybedford]

On @joyeecheung's advice I've gone ahead and changed the way the async bootstrap works. Instead of always applying an async bootstrap, the async bootstrap and all promises associated will only apply lazily when the ESM loader is actually in use. This way loading CommonJS retains a fully sync bootstrap that is completely backwards compatible with no timings changes or task queue differences.

This also removes the dependence of this work on #29848.

All tests are now passing! Further review welcome.

[guybedford]

I've split out the bootstrap changes into a separate PR at #29937, and based this unflagging to that PR for a simpler diff.

[MylesBorins]

We likely want #29974 to land as well

[MylesBorins]

@nodejs/modules anyone have an issue with renaming --loader to --experimental-loader before we land this? I can open a PR (and 12.x backport), but I'd be concerned with unflagging and not being explicit about this