perf(build): Use WebWorker when removing private fields

[miyaji255]

removePrivateFields is a heavy CPU-bound process. This PR improves performance by using all CPU in WebWorker.

The following is the removePrivateFields time for the current build process.

Environemt:

• CPU: Intel(R) Core(TM) i7-12700F (20 Cores)
• RAM: 32GB

Current: 47750.3256ms
This PR: 10963.4007ms

The Github Actions environment is 4 CPUs, so CI may not improve performance that much. I think it will be very fast in local environment.

[codecov]

Codecov Report

Attention: Patch coverage is 48.91304% with 47 lines in your changes missing coverage. Please review.

Project coverage is 91.30%. Comparing base (2ead4d8) to head (36f2a72).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
build/remove-private-fields.ts	0.00%	32 Missing ⚠️
build/remove-private-fields-worker.ts	75.00%	15 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3821      +/-   ##
==========================================
- Coverage   91.71%   91.30%   -0.41%     
==========================================
  Files         160      161       +1     
  Lines       10195    10241      +46     
  Branches     2885     2848      -37     
==========================================
+ Hits         9350     9351       +1     
- Misses        844      889      +45     
  Partials        1        1              

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[yusukebe]

Hi @miyaji255

This is super cool! I've tried it, and it's working very fast on my machine. I love this change.

@nakasyou Can you review this PR?

[nakasyou]

Yes but about a day please🙏

[yusukebe]

@nakasyou No problem!

[nakasyou]

It looks good! Check my review.

[yusukebe]

LGTM!

[yusukebe]

@miyaji255

Thank you for your great work! Merging.