fix: support userAgent option for jsdom environment

[nwalters512]

Summary

In older versions of jsdom, it was possible to specify a custom userAgent in the JSDOM constructor options. In Jest, that could be set with testEnvironmentOptions, which would be passed as options to the Jest constructor. The Jest docs even specifically call out this example: https://github.com/facebook/jest/blame/6df4ad4a8eb4f63fa4580d6f5664f43762940379/docs/Configuration.md#L1132.

However, jsdom removed this option at some point in a minor release of v12 in this commit. When we went to upgrade Jest to a newer version, many of our tests started failing because jsdom's default user agent was being used instead of the one we had specified.

As called out in this comment, it's possible to work around this by setting up a custom testing environment, but I'd hate to have to copy that boilerplate around to all of the repos where we need to customize the user agent. So, I'm proposing this change.

This change should be safe; for the past several major versions of jsdom, the userAgent option to the constructor has been a no-op, so this should be considered a feature addition as opposed to a breaking change. If someone had previously set userAgent in testEnvironmentOptions, it would start taking effect with this change where it hadn't previously; that's the only risk to this I can think of.

Test plan

I edited the code in node_modules in my project to reflect these changes, and it worked as expected! I also added a test case, which passes.

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[nwalters512]

Just signed the CLA 📝

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[sigveio]

A changelog entry appears to be missing 🙂

[nwalters512]

A changelog entry appears to be missing 🙂

Thanks for the reminder! I was waiting until the PR was open so I could grab the link to it. Should be all set now 🙂

[codecov-commenter]

Codecov Report

Merging #11773 (953ca86) into master (84b3b03) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #11773      +/-   ##
==========================================
- Coverage   69.01%   69.01%   -0.01%     
==========================================
  Files         312      312              
  Lines       16339    16341       +2     
  Branches     4736     4738       +2     
==========================================
+ Hits        11276    11277       +1     
- Misses       5035     5036       +1     
  Partials       28       28              

Impacted Files	Coverage Δ
packages/jest-environment-jsdom/src/index.ts	41.81% <100.00%> (+2.19%)	⬆️
packages/expect/src/utils.ts	95.58% <0.00%> (-0.56%)	⬇️

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[SimenB]

Thanks! I think this is a bug fix as you say 🙂

[nwalters512]

🙌 thanks for getting this merged quickly and fixing up my lint errors - apologies, I missed those locally!

[SimenB]

No problem, thanks for taking the time to send a PR 🙂 CI was supposed to tell you about the lint stuff, but since GH doesn't run actions for first time contributors without a maintainer hitting the button it never happened

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