Add implementations for ctags rebuildOnStart and rebuildOnFileSave

[kimadeline]

For #793

• 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.

[codecov-io]

Codecov Report

Merging #8889 into master will increase coverage by 0.12%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##           master    #8889      +/-   ##
==========================================
+ Coverage   57.95%   58.07%   +0.12%     
==========================================
  Files         527      527              
  Lines       27532    27548      +16     
  Branches     4146     4150       +4     
==========================================
+ Hits        15955    15998      +43     
+ Misses      10700    10665      -35     
- Partials      877      885       +8

Impacted Files	Coverage Δ
src/client/workspaceSymbols/main.ts	64.28% <83.33%> (+48.1%)	⬆️

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[karrtikr]

Nicely done👏
Earlier, I would've used sinon to directly mock out this.buildWorkspaceSymbols(...) method. But I assume you're testing it like this because of the testing discussion that we had?