Kill child processes of a Kernel process when existing Kernel Proc

[DonJayamanne]

Fixes #11018

To be reviewed after merging #11132

[codecov-commenter]

Codecov Report

Merging #11133 (8a0ddcc) into main (8c56132) will decrease coverage by 0%.
The diff coverage is 86%.

❗ Current head 8a0ddcc differs from pull request most recent head 125395b. Consider uploading reports for the commit 125395b to get more accurate results

@@          Coverage Diff           @@
##            main   #11133   +/-   ##
======================================
- Coverage     63%      63%   -1%     
======================================
  Files        482      482           
  Lines      33960    33981   +21     
  Branches    5541     5545    +4     
======================================
+ Hits       21492    21494    +2     
- Misses     10411    10429   +18     
- Partials    2057     2058    +1     

Impacted Files	Coverage Δ
src/kernels/raw/types.ts	100% <ø> (ø)
src/kernels/raw/launcher/kernelProcess.node.ts	71% <69%> (-1%)	⬇️
src/interactive-window/interactiveWindow.ts	74% <100%> (ø)
...c/kernels/execution/cellExecutionMessageHandler.ts	77% <100%> (-1%)	⬇️
src/kernels/helpers.ts	60% <100%> (+<1%)	⬆️
src/kernels/jupyter/launcher/jupyterExecution.ts	63% <100%> (ø)
...jupyter/launcher/liveshare/hostJupyterExecution.ts	87% <100%> (ø)
...c/kernels/jupyter/launcher/notebookStarter.node.ts	68% <100%> (ø)
...kernels/jupyter/session/backingFileCreator.base.ts	68% <100%> (ø)
...nels/jupyter/session/jupyterRequestCreator.node.ts	57% <100%> (ø)
... and 30 more