Use file system API for path comparisons when performing code navigation

[DonJayamanne]

Fixes #1811

This pull request:

• Has a title summarizes what is changing
• Includes a news entry file (remember to thank yourself!)
• Has unit tests & code coverage is not adversely affected (within reason)
• 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)

[brettcannon]

We should @bstaint co-authorship credit for finding the root cause.

[brettcannon]

https://help.github.com/articles/creating-a-commit-with-multiple-authors/

[codecov]

Codecov Report

Merging #1812 into master will decrease coverage by 0.13%.
The diff coverage is 61.9%.

@@ Coverage Diff @@ ## master #1812 +/- ## ========================================== - Coverage 74.37% 74.23% -0.14%  ========================================== Files 282 282 Lines 13218 13144 -74 Branches 2375 2357 -18 ========================================== - Hits 9831 9758 -73  + Misses 3256 3253 -3  - Partials 131 133 +2

Impacted Files	Coverage Δ
src/client/activation/classic.ts	91.83% <100%> (+0.53%)	⬆️
src/client/providers/symbolProvider.ts	59.37% <57.89%> (-22.63%)	⬇️
src/client/language/braceCounter.ts	81.08% <0%> (-13.52%)	⬇️
src/client/common/variables/environment.ts	92.45% <0%> (-4.92%)	⬇️
src/client/debugger/PythonProcess.ts	49.58% <0%> (-1.67%)	⬇️
src/client/interpreter/locators/index.ts	90% <0%> (-1.49%)	⬇️
...lient/debugger/configProviders/pythonV2Provider.ts	83.33% <0%> (-1.05%)	⬇️
src/client/extension.ts	96.96% <0%> (-0.05%)	⬇️
src/client/common/types.ts	100% <0%> (ø)	⬆️
... and 12 more

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[brettcannon]

So bstaint said they didn't want to sign the CLA, so I tweaked the phrasing to say he provided a diagnosis of the problem since we didn't directly take any code from them.