fix: set require.main when importing CJS from ESM

[jablko]

For ESM tests, jestAdapter() calls Runtime.unstable_importModule() -> Runtime.loadEsmModule():
https://github.com/facebook/jest/blob/d38156ccd7a68e52372b4eb6fc02afbadd5b703e/packages/jest-circus/src/legacy-code-todo-rewrite/jestAdapter.ts#L74-L78

It doesn't call Runtime.requireModule() -> Runtime._loadModule() -> Runtime._execModule(), so it doesn't set Runtime._mainModule/require.main:
https://github.com/facebook/jest/blob/d38156ccd7a68e52372b4eb6fc02afbadd5b703e/packages/jest-runtime/src/index.ts#L1205-L1207

Consequently require.main is null:

 FAIL  test/index.test.js
  ● Test suite failed to run

    TypeError: Cannot read property 'filename' of null

I haven't investigated whether this changed in #10621 (whether previously require.main was always undefined, or only when using isolateModules(), ∴ regression?). Either way, this PR proposes to copy this._mainModule = module to the ESM code path.

I'm not sure where is the "right" location -- between loadEsmModule() and linkAndEvaluateModule() seemed analogous to the existing location in Runtime._execModule()?

[codecov-commenter]

Codecov Report

Merging #11790 (3847dc7) into master (d38156c) will decrease coverage by 0.00%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master   #11790      +/-   ##
==========================================
- Coverage   69.01%   69.00%   -0.01%     
==========================================
  Files         312      312              
  Lines       16346    16348       +2     
  Branches     4742     4743       +1     
==========================================
  Hits        11281    11281              
- Misses       5037     5039       +2     
  Partials       28       28              

Impacted Files	Coverage Δ
packages/jest-runtime/src/index.ts	58.62% <0.00%> (-0.16%)	⬇️

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[SimenB]

Where you added it here seems fine to me 🙂 Could you add a test as well? Plus a changelog entry

[SimenB]

@jablko ping 🙂

[SimenB]

Based on https://nodejs.org/api/modules.html#accessing-the-main-module

When the entry point is not a CommonJS module, require.main is undefined, and the main module is out of reach.

I think the current behaviour is correct when the entry point is ESM

[github-actions]

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