Change Promise detection code in jest-circus to support non-global Promise implementations

[suchipi]

Summary

This isn't related to any particular open issue with jest-circus, but I noticed it while reading through the code to familiarize myself with it, and so decided to submit it on the side as a small improvement.

To provide better interop for Promise libraries such as bluebird and Q, this changes
the part of jest-circus that detects a returned Promise from a test or hook to only
check that the value is an object with a then method on it, rather than checking that
the value is instanceof Promise. This is considered the standard way of checking for
a Promises/A+-compliant Promise. As an added bonus, this check works cross-realm.

Test plan

I think we should add an integration test to this that pulls in bluebird, Q, or jQuery deferred, and verifies that the test runs as expected, but I'm not sure how to add an integration test that has a dependency like that. Should it be a dev dependency of the whole project?

[codecov-io]

Codecov Report

Merging #4375 into master will decrease coverage by 0.35%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #4375      +/-   ##
==========================================
- Coverage    56.2%   55.85%   -0.36%     
==========================================
  Files         191      189       -2     
  Lines        6421     6383      -38     
  Branches        6        6              
==========================================
- Hits         3609     3565      -44     
- Misses       2809     2815       +6     
  Partials        3        3

Impacted Files	Coverage Δ
packages/jest-circus/src/utils.js	0% <0%> (ø)	⬆️
...ckages/jest-cli/src/reporters/get_result_header.js	78.57% <0%> (-3.79%)	⬇️
...ackages/jest-cli/src/reporters/default_reporter.js	91.04% <0%> (-0.39%)	⬇️
packages/jest-cli/src/reporters/Status.js	93.75% <0%> (-0.19%)	⬇️
packages/jest-config/src/normalize.js	78.26% <0%> (ø)	⬆️
packages/jest-config/src/index.js	0% <0%> (ø)	⬆️
...ges/jest-cli/src/reporters/get_snapshot_summary.js
...ages/jest-cli/src/reporters/get_snapshot_status.js
packages/jest-cli/src/reporters/utils.js	62.5% <0%> (+1.11%)	⬆️
...ackages/jest-cli/src/reporters/summary_reporter.js	19.69% <0%> (+7.69%)	⬆️

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[cpojer]

Nice! I updated the comment a bit to not mention specific custom Promise implementations as those ones likely won't be relevant in the future.

[suchipi]

Do we want to add a test for this?

[cpojer]

Yes, if you want to add some. The old code already does this, so it's simply aligning the implementation but explicit tests are always good.

[suchipi]

I started writing some tests for this but ran into some weirdness around #3785. I don't want to add tests that don't pass with jasmine, but pass with circus, so I'll defer adding tests for this until circus is the only runner.

[github-actions]

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