Cache the result of ipykernel dependency check

[DonJayamanne]

Part of #7849

• If we've check if IPyKernel is installed, then cache that
• If IPyKernel isn't installed & kernel startup fails, ensure we double check if IPyKernel is installed & prompt the user to install that

[codecov-commenter]

Codecov Report

Merging #8282 (9fbef80) into main (0b96df1) will decrease coverage by 0%.
The diff coverage is 55%.

@@          Coverage Diff          @@
##            main   #8282   +/-   ##
=====================================
- Coverage     72%     72%   -1%     
=====================================
  Files        371     371           
  Lines      23034   23055   +21     
  Branches    3505    3510    +5     
=====================================
+ Hits       16620   16633   +13     
- Misses      4979    4984    +5     
- Partials    1435    1438    +3     

Impacted Files	Coverage Δ
src/client/datascience/errors/errorHandler.ts	64% <0%> (-3%)	⬇️
src/client/datascience/types.ts	100% <ø> (ø)
src/client/common/errors/errorUtils.ts	65% <11%> (-5%)	⬇️
src/client/common/installer/productInstaller.ts	61% <100%> (+2%)	⬆️
...science/jupyter/kernels/kernelDependencyService.ts	82% <100%> (+1%)	⬆️
src/client/common/application/webviews/webview.ts	73% <0%> (-2%)	⬇️
...lient/datascience/jupyter/kernels/cellExecution.ts	73% <0%> (-1%)	⬇️
src/client/datascience/raw-kernel/rawSocket.ts	84% <0%> (+1%)	⬆️
...ook/intellisense/pythonKernelCompletionProvider.ts	76% <0%> (+3%)	⬆️