Disconnect form debugger if user deletes cell while debugging

[DavidKutu]

For #7631

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR).
• Title summarizes what is changing.
• Has a news entry file (remember to thank yourself!).
• Appropriate comments and documentation strings in the code.
• Has sufficient logging.
• Has telemetry for enhancements.
• Unit tests & system/integration tests are added/updated.
• Test plan is updated as appropriate.
• package-lock.json has been regenerated by running npm install (if dependencies have changed).

[codecov-commenter]

Codecov Report

Merging #7666 (7239e16) into main (a8aeaac) will increase coverage by 0%.
The diff coverage is 37%.

@@          Coverage Diff          @@
##            main   #7666   +/-   ##
=====================================
  Coverage     68%     68%           
=====================================
  Files        363     363           
  Lines      22552   22562   +10     
  Branches    3432    3432           
=====================================
+ Hits       15467   15498   +31     
+ Misses      5747    5730   -17     
+ Partials    1338    1334    -4     

Impacted Files	Coverage Δ
src/client/debugger/jupyter/kernelDebugAdapter.ts	79% <37%> (-3%)	⬇️
...datascience/editor-integration/codelensprovider.ts	69% <0%> (-2%)	⬇️
src/client/datascience/jupyter/jupyterNotebook.ts	25% <0%> (-1%)	⬇️
src/client/datascience/commands/commandRegistry.ts	35% <0%> (-1%)	⬇️
src/client/datascience/webviews/webviewHost.ts	77% <0%> (ø)
src/client/datascience/constants.ts	99% <0%> (+<1%)	⬆️
...client/datascience/commands/activeEditorContext.ts	91% <0%> (+<1%)	⬆️
...lient/datascience/variablesView/notebookWatcher.ts	88% <0%> (+1%)	⬆️
src/client/datascience/jupyter/kernels/kernel.ts	75% <0%> (+2%)	⬆️
...ence/editor-integration/cellHashProviderFactory.ts	100% <0%> (+2%)	⬆️
... and 2 more

[DonJayamanne]

Rather than storing the debugCellUri, you might as well store the reference to the cell object.
Then just compare if (cell === this.debugCell)
that will be better (else you end up comparing uris everytime).