LS settings for typeshed and diagnostics

[MikhailArkhipov]

Fixes #2030

Adds options to control diagnostics
Adds option to 'open files only'
Adds option for typeshed paths
Controls when to restart LS so we we don't reload on trivial settings change

This pull request:

• Has a title summarizes what is changing
• Works on all actively maintained versions of Python (e.g. Python 2.7 & the latest Python 3 release)
• Works on Windows 10, macOS, and Linux (e.g. considered file system case-sensitivity)

Tests are to be added on PTVS side, I can add one integration test to VSC.

[codecov]

Codecov Report

Merging #2065 into master will decrease coverage by 0.13%.
The diff coverage is 26.66%.

@@            Coverage Diff             @@
##           master    #2065      +/-   ##
==========================================
- Coverage   79.95%   79.82%   -0.14%     
==========================================
  Files         307      307              
  Lines       14064    14086      +22     
  Branches     2494     2499       +5     
==========================================
- Hits        11245    11244       -1     
- Misses       2807     2830      +23     
  Partials       12       12

Flag	Coverage Δ
#MacOS	74% <26.66%> (-0.09%)	⬇️
#Windows	74.08% <26.66%> (-0.1%)	⬇️

Impacted Files	Coverage Δ
src/client/common/types.ts	100% <ø> (ø)	⬆️
src/client/common/configSettings.ts	91.52% <100%> (+0.19%)	⬆️
src/client/activation/analysis.ts	25.86% <19.51%> (-2.35%)	⬇️
...unittests/common/testVisitors/flatteningVisitor.ts	84.61% <0%> (-2.57%)	⬇️
src/client/interpreter/helpers.ts	88.37% <0%> (-2.33%)	⬇️
src/client/common/process/pythonProcess.ts	93.18% <0%> (-2.28%)	⬇️
...reter/locators/services/cacheableLocatorService.ts	93.87% <0%> (-2.05%)	⬇️
src/client/common/platform/fileSystem.ts	71.42% <0%> (-1.2%)	⬇️
src/client/interpreter/interpreterService.ts	81.05% <0%> (-1.06%)	⬇️
src/client/unittests/main.ts	46.69% <0%> (ø)	⬆️
... and 2 more

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