Support rootDir tag in testEnvironment

[thymikee]

Summary

rootDir was not replaced in custom testEnvironment, so it was harder to use custom unpublished environments. This PR fixes it.

Test plan

Added a test.

[codecov-io]

Codecov Report

Merging #4579 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #4579      +/-   ##
==========================================
+ Coverage   55.63%   55.65%   +0.01%     
==========================================
  Files         186      186              
  Lines        6348     6348              
  Branches        3        3              
==========================================
+ Hits         3532     3533       +1     
+ Misses       2815     2814       -1     
  Partials        1        1

Impacted Files	Coverage Δ
packages/jest-config/src/utils.js	75% <100%> (+2.27%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b430e51...8591a9d. Read the comment docs.

[cpojer]

Oh yeah, that's a bug! Good seeing you @thymikee :)

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.
Please note this issue tracker is not a help forum. We recommend using StackOverflow or our discord channel for questions.