Add restart language server command

[jakebailey]

For #3073

Uses the existing language server restarting mechanism, which is already used for things like interpreter changes and such.

• 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).
• The wiki is updated with any design decisions/details.

[luabud]

command name LGTM

[Hubro]

Yes! Please somebody tag someone with write access to review this, I have been annoyed by the absence of this command for so long.

@jakebailey Oh I just noticed you're on the language server team, never mind me then. You got this :)

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities (and 0 Security Hotspots to review)
0 Code Smells

No Coverage information
0.0% Duplication

[codecov-commenter]

Codecov Report

Merging #12952 into master will decrease coverage by 0.03%.
The diff coverage is 57.14%.

@@            Coverage Diff             @@
##           master   #12952      +/-   ##
==========================================
- Coverage   59.81%   59.78%   -0.04%     
==========================================
  Files         670      670              
  Lines       37163    37183      +20     
  Branches     5264     5265       +1     
==========================================
- Hits        22230    22228       -2     
- Misses      13805    13824      +19     
- Partials     1128     1131       +3     

Impacted Files	Coverage Δ
src/client/activation/node/manager.ts	27.86% <33.33%> (+1.08%)	⬆️
src/client/activation/languageServer/manager.ts	81.15% <66.66%> (-1.66%)	⬇️
src/client/activation/activationService.ts	89.72% <100.00%> (ø)
src/client/activation/commands.ts	100.00% <100.00%> (ø)
src/client/common/utils/platform.ts	64.70% <0.00%> (-11.77%)	⬇️
src/client/datascience/crossProcessLock.ts	79.41% <0.00%> (-11.77%)	⬇️
...datascience/interactive-common/notebookProvider.ts	50.58% <0.00%> (-4.68%)	⬇️
src/client/linters/pydocstyle.ts	86.66% <0.00%> (-2.23%)	⬇️
src/client/datascience/debugLocationTracker.ts	76.56% <0.00%> (-1.57%)	⬇️
src/client/common/process/proc.ts	14.49% <0.00%> (-0.73%)	⬇️
... and 1 more

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[karrtikr]

LGTM