Limit suspension to a single thread

[jbdoderlein]

This PR is a solution to #2570

It limit the suspension in the debugger to a single thread only. If a thread is suspended, all other thread continues their execution and skips any suspension request.

This is the more concise and less-impacting solution I found for #2570, as it correct the issue, and still allow debugging code inside web server.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 46%. Comparing base (105e440) to head (a2919ca).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/org/rascalmpl/debug/DebugHandler.java	0%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##              main   #2573   +/-   ##
=======================================
- Coverage       46%     46%   -1%     
+ Complexity    6617    6616    -1     
=======================================
  Files          792     792           
  Lines        65396   65399    +3     
  Branches      9792    9793    +1     
=======================================
- Hits         30470   30464    -6     
- Misses       32573   32579    +6     
- Partials      2353    2356    +3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.