fix: graceful shutdown on watch/cache

[evenstensberg]

What kind of change does this PR introduce?

#3075

Did you add tests for your changes?
TBD

If relevant, did you update the documentation?
TBD
Summary

Does this PR introduce a breaking change?

No

Other information

Need to add tests.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.70%. Comparing base (f407b24) to head (f29d6e8).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4546      +/-   ##
==========================================
+ Coverage   89.68%   89.70%   +0.02%     
==========================================
  Files           9        9              
  Lines        1396     1399       +3     
  Branches      445      447       +2     
==========================================
+ Hits         1252     1255       +3     
  Misses        144      144              

Files with missing lines	Coverage Δ
packages/webpack-cli/src/webpack-cli.ts	90.70% <100.00%> (+0.02%)	⬆️

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[alexander-akait]

We should include this in the next major release, not now, and please add a test case

[evenstensberg]

Still wip, need to send a sigterm signal whenever.

[evenstensberg]

after compile is done and we got an async plugin the sigterm is invoked while we're in the child process without an infinite loop fyi @alexander-akait

[evenstensberg]

Might need to specify cache.type in the check at isFileSystemCacheEnabled