Use eshost to run tests in multiple engines

[mhofman]

https://github.com/bterlson/eshost allows running code in different agents / engines. It would be great to run endo tests in all engines to make sure no implementations exhibit unexpected behavior.

[mhofman]

@kriskowal I believe this would be subsumed by moving to test262 and a runner based on eshost?

[kriskowal]

Certainly overlaps:

• SES test262 conformance suite #870
• Ava Test 262 runner #1001
• Sync XS interpretation of dynamic module loading #1066

Those issues could be reframed as this one. We need something parody of eshost that runs on every engine with SES shim pre-initialized.

[kriskowal]

With #1847 we have a place to stand for adding these tests.