test_runner: add getTestContext() public API

[MoLow]

Exposes getTestContext() function to access test context information from within tests and async operations.

My use case was exposing a pino logger that writes to test diagnostics, but there can be many other usecases:

import { prettyFactory } from 'pino-pretty';

const pretty = prettyFactory({ colorize: true  });
const asyncId = executionAsyncId();
const t = testResources.get(asyncId);
t.diagnostic(pretty(obj).replace(/\n$/, ''));

[nodejs-github-bot]

Review requested:

• @nodejs/test_runner

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/72266/

[codecov]

Codecov Report

❌ Patch coverage is 70.83333% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.71%. Comparing base (d9645d7) to head (28d1af6).
⚠️ Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/test_runner/harness.js	65.00%	6 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #62501      +/-   ##
==========================================
+ Coverage   89.69%   89.71%   +0.01%     
==========================================
  Files         692      692              
  Lines      214039   214061      +22     
  Branches    41064    41066       +2     
==========================================
+ Hits       191985   192037      +52     
+ Misses      14134    14098      -36     
- Partials     7920     7926       +6     

Files with missing lines	Coverage Δ
lib/internal/test_runner/test.js	96.80% <100.00%> (+<0.01%)	⬆️
lib/test.js	100.00% <100.00%> (ø)
lib/internal/test_runner/harness.js	86.14% <65.00%> (-0.99%)	⬇️

... and 36 files with indirect coverage changes

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[ljharb]

I think this could be used by malicious code to behave well in tests, and then behave badly in prod. it'd be different if it was like t.getContext(), though, because malicious code wouldn't have access to t. As it is, it feels like an implicit global communications channel, and those are not advisable.

Only requesting changes to ensure that with multiple stamps, it doesn't land until this item is discussed.