Support "pathMappings" in "launch" debug configs.

[ericsnowcurrently]

(for #3568)

• 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 #7024 into master will increase coverage by 0.08%.
The diff coverage is 86.27%.

@@            Coverage Diff             @@
##           master    #7024      +/-   ##
==========================================
+ Coverage   58.29%   58.38%   +0.08%     
==========================================
  Files         483      483              
  Lines       21347    21421      +74     
  Branches     3445     3474      +29     
==========================================
+ Hits        12445    12507      +62     
- Misses       8124     8141      +17     
+ Partials      778      773       -5

Impacted Files	Coverage Δ
src/client/debugger/types.ts	100% <ø> (ø)	⬆️
...bugger/extension/configuration/resolvers/attach.ts	79.24% <100%> (-3.3%)	⬇️
src/client/common/platform/platformService.ts	33.33% <33.33%> (-9.17%)	⬇️
src/client/common/utils/platform.ts	88.23% <75%> (-11.77%)	⬇️
...bugger/extension/configuration/resolvers/launch.ts	88.09% <77.77%> (-1.52%)	⬇️
...debugger/extension/configuration/resolvers/base.ts	96.77% <94.73%> (-1.01%)	⬇️
src/client/common/logger.ts	68.55% <0%> (-4.41%)	⬇️
src/client/linters/baseLinter.ts	80.34% <0%> (-1.37%)	⬇️
...atascience/interactive-window/interactiveWindow.ts	7.38% <0%> (-0.04%)	⬇️
src/client/common/configSettings.ts	57.54% <0%> (ø)	⬆️
... and 6 more

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[karrtikr]

I would like to understand the test code before merging it. Things seem a bit magical.

[ericsnowcurrently]

As far as I can tell, the current CI failures here are unrelated to this PR.

[karrtikr]

@ericsnowcurrently You will have to rebase from master branch.