Do not dispose kernel message handler for a cell when cell completes execution

[DonJayamanne]

Fixes #11526

[codecov-commenter]

Codecov Report

Merging #11542 (b7932d9) into main (c06b44d) will increase coverage by 0%.
The diff coverage is n/a.

@@          Coverage Diff           @@
##            main   #11542   +/-   ##
======================================
  Coverage     63%      63%           
======================================
  Files        477      477           
  Lines      34059    34058    -1     
  Branches    5527     5526    -1     
======================================
+ Hits       21507    21519   +12     
+ Misses     10497    10481   -16     
- Partials    2055     2058    +3     

Impacted Files	Coverage Δ
src/kernels/execution/cellExecution.ts	72% <ø> (-1%)	⬇️
src/kernels/execution/notebookUpdater.ts	88% <0%> (-8%)	⬇️
src/platform/common/cancellation.ts	64% <0%> (-4%)	⬇️
src/kernels/jupyter/jupyterKernelService.node.ts	72% <0%> (-2%)	⬇️
src/platform/common/utils/decorators.ts	91% <0%> (+<1%)	⬆️
...c/kernels/execution/cellExecutionMessageHandler.ts	78% <0%> (+1%)	⬆️
src/kernels/raw/finder/localKernelFinder.node.ts	76% <0%> (+1%)	⬆️
src/kernels/helpers.ts	68% <0%> (+1%)	⬆️
src/platform/common/utils/async.ts	51% <0%> (+1%)	⬆️
.../standalone/survey/dataScienceSurveyBanner.node.ts	71% <0%> (+5%)	⬆️