Features to support test adapter extension

[Samirat]

I've been working on a C# adapter for Test Explorer UI. This adds features to OmniSharp to support that.

My adapter: https://github.com/Samirat/omnisharp-test-adapter

In particular this adds:

1. A DiscoverTests request, which lets you get information about all tests in an assembly
2. A NoBuild option for all test requests, which lets you run/debug tests without always building them first
3. An extension export for the TestManager

I've got a separate PR for the runsettings thing, but it was difficult to extract from this branch, so those changes are included here.

[codecov]

Codecov Report

Merging #3601 into master will increase coverage by 2.88%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3601      +/-   ##
==========================================
+ Coverage   86.92%   89.81%   +2.88%     
==========================================
  Files          59       59              
  Lines        1805     1590     -215     
  Branches      208       89     -119     
==========================================
- Hits         1569     1428     -141     
+ Misses        181      151      -30     
+ Partials       55       11      -44     

Flag	Coverage Δ
#integration	100.00% <ø> (ø)
#unit	89.81% <100.00%> (+2.88%)	⬆️

Impacted Files	Coverage Δ
src/omnisharp/protocol.ts	83.76% <100.00%> (+6.06%)	⬆️
src/observers/utils/ShowErrorMessage.ts	66.66% <0.00%> (-8.34%)	⬇️
src/observers/utils/ShowWarningMessage.ts	80.00% <0.00%> (-3.34%)	⬇️
src/observers/utils/ShowInformationMessage.ts	80.00% <0.00%> (-3.34%)	⬇️
src/coreclr-debug/ParsedEnvironmentFile.ts	84.00% <0.00%> (-2.67%)	⬇️
src/omnisharp/options.ts	92.64% <0.00%> (-1.68%)	⬇️
src/observers/OmnisharpDebugModeLoggerObserver.ts	86.04% <0.00%> (-1.19%)	⬇️
src/observers/CsharpLoggerObserver.ts	86.15% <0.00%> (-0.81%)	⬇️
src/omnisharp/loggingEvents.ts	97.92% <0.00%> (-0.07%)	⬇️
src/omnisharp/EventType.ts	100.00% <0.00%> (ø)
... and 43 more

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[JoeRobich]

Thanks! I look forward to trying this out in test explorer. These changes look good to me.

[JoeRobich]

@Samirat Sorry I tried fixing merge conflicts and inadvertently broke the package-lock.json. I can't seem to push changes to the PR branch, but running npm i and pushing the changes should resolve this.

[Samirat]

@JoeRobich Thanks for the review. I probably need to check this over before merging anyway, make sure I didn't leave it any test code or anything. I'll take a look and get it ready to go tomorrow.

We've been using the test explorer adapter for a while, and it works pretty well. The one thing that would be really nice is test cancellation support, but it seemed like this might be kind of complicated to add right now.

[JoeRobich]

@Samirat I believe this (#3796) will fix the build errors you are seeing. The new TS compiler brought in with npm i is more correct about the Package type.

[JoeRobich]

@Samirat Thanks!