test: move coverage source map tests to new file

[avivkeller]

This PR moves the coverage source map tests to their own file / fixture folders.

Why?

Currently, source map support in the test runner has a few bugs (such as...), and with the future bugfixes, additional tests will be added.

The test coverage test file is very large, the additional tests will make it even larger, so this PR moves the sourcemap tests to their own file, so it can expand healthily.

[nodejs-github-bot]

Review requested:

• [ ] @nodejs/test_runner

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 88.24%. Comparing base (aac8ba7) to head (eb755c1). Report is 379 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #55123      +/-   ##
==========================================
- Coverage   88.24%   88.24%   -0.01%     
==========================================
  Files         651      651              
  Lines      183856   183856              
  Branches    35853    35852       -1     
==========================================
- Hits       162251   162245       -6     
- Misses      14896    14899       +3     
- Partials     6709     6712       +3     

see 33 files with indirect coverage changes

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/62850/

[nodejs-github-bot]

Landed in 1d95b79b6688fcb6a800c5a70f274fa6d7b23181