CTRL+Z should not undo at the top level

[rchiodo]

For #7999

CTRL+Z was not being checked separately from just plain 'Z'

[codecov-io]

Codecov Report

Merging #8571 into master will increase coverage by 0.34%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #8571      +/-   ##
==========================================
+ Coverage   58.72%   59.07%   +0.34%     
==========================================
  Files         511      511              
  Lines       23328    23699     +371     
  Branches     3829     3829              
==========================================
+ Hits        13700    14000     +300     
- Misses       8709     8780      +71     
  Partials      919      919

Impacted Files	Coverage Δ
...ience/interactive-common/interactiveWindowTypes.ts	100% <100%> (ø)	⬆️
src/client/testing/serviceRegistry.ts	48.64% <0%> (-44.21%)	⬇️
...t/datascience/jupyter/jupyterDataRateLimitError.ts	66.66% <0%> (-33.34%)	⬇️
src/client/formatters/serviceRegistry.ts	75% <0%> (-25%)	⬇️
...ience/jupyter/jupyterDebuggerRemoteNotSupported.ts	75% <0%> (-25%)	⬇️
src/client/common/utils/icons.ts	83.33% <0%> (-16.67%)	⬇️
src/client/testing/codeLenses/main.ts	44.44% <0%> (-15.56%)	⬇️
src/client/api.ts	78.57% <0%> (-11.43%)	⬇️
src/client/common/utils/version.ts	77.77% <0%> (-1.39%)	⬇️
src/client/providers/providerUtilities.ts	83.33% <0%> (-1.29%)	⬇️
... and 29 more

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