re-use the same codeWatcher when providing code lenses

[amunger]

Fixes #8919

We can just update the code lenses for the new version of the document.
The codeWatcher doesn't use the settings that it was holding, so we can stop deserializing that every time.

• 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 #9221 (b068c09) into main (febcb8a) will increase coverage by 0%.
The diff coverage is 100%.

❗ Current head b068c09 differs from pull request most recent head 81cc34c. Consider uploading reports for the commit 81cc34c to get more accurate results

@@          Coverage Diff          @@
##            main   #9221   +/-   ##
=====================================
  Coverage     71%     71%           
=====================================
  Files        383     383           
  Lines      24779   24773    -6     
  Branches    3985    3983    -2     
=====================================
- Hits       17737   17735    -2     
+ Misses      5447    5442    -5     
- Partials    1595    1596    +1     

Impacted Files	Coverage Δ
src/client/datascience/types.ts	100% <ø> (ø)
...datascience/editor-integration/codelensprovider.ts	83% <100%> (+<1%)	⬆️
...ient/datascience/editor-integration/codewatcher.ts	70% <100%> (+<1%)	⬆️
...lient/datascience/jupyter/kernels/cellExecution.ts	73% <0%> (-1%)	⬇️
...atascience/interactive-window/interactiveWindow.ts	69% <0%> (-1%)	⬇️
src/client/datascience/jupyter/kernels/helpers.ts	55% <0%> (+<1%)	⬆️
...t/datascience/notebook/vscodeNotebookController.ts	79% <0%> (+1%)	⬆️