Ensure debugged program is terminated when Stop debugging button is clicked

[DonJayamanne]

Fixes #1345

This pull request:

• Has a title summarizes what is changing
• Includes a news entry file (remember to thank yourself!)

[codecov]

Codecov Report

Merging #1739 into master will increase coverage by 0.13%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1739      +/-   ##
==========================================
+ Coverage   73.56%   73.69%   +0.13%     
==========================================
  Files         279      279              
  Lines       13060    13060              
  Branches     2328     2328              
==========================================
+ Hits         9607     9624      +17     
+ Misses       3314     3304      -10     
+ Partials      139      132       -7

Impacted Files	Coverage Δ
src/client/debugger/Main.ts	52.34% <0%> (+0.49%)	⬆️
src/client/debugger/mainV2.ts	78.71% <0%> (+0.8%)	⬆️
src/client/debugger/PythonProcess.ts	51.25% <0%> (+5.41%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9022527...13dfe18. Read the comment docs.