WIP: mocha and lighthouse-core as esm

[connorjclark]

As requested, this combines these two large branches:

• mocha-final tests: replace jest with mocha #14054
• esm-core (no PR yet)

Some issues cropped up that are still unresolved, but aren't showstoppers. Namely:

• Random test failure,

  lighthouse/lighthouse-core/test/fraggle-rock/gather/navigation-runner-test.js

  Line 425 in ce17c7d

  it.skip('finds page load errors in network records when available', async () => {

• errors that are certainly LighthouseErrors are failing instanceof check

  lighthouse/lighthouse-core/runner.js

  Line 443 in ce17c7d

  // yarn mocha navigation-runner-test -t 'includes a top-level runtimeError when a gatherer throws one'

  lighthouse/lighthouse-core/fraggle-rock/gather/navigation-runner.js

  Line 108 in ce17c7d

  // yarn mocha navigation-runner-test -t 'should retain PageLoadError'

[connorjclark]

Sigh...

The tests pass locally, I swear. I'm sure they'll pass in CI too...