Convert unit tests to Typescript

[kravets-levko]

Part of PECO-1390

Initially I planned to convert unit tests gradually, but there were issues with collecting coverage data. So I had to convert everything at once

[benc-db]

Ideally we test through the public interface. Do we need to expose these to get reasonable test coverage? I don't know the standards in the Node world, but in general my approach is, if there are methods that should be private, but I need to expose in order to test, I make a new type where those methods make sense as public methods, and have the original type call the new type to accomplish the work. This allows you to mock the new class in the tests of the original class, and not feel compelled to have a large public interface that consumers really shouldn't call. Given how big a change we are already doing, I won't block this PR on that, but it's something we should consider before we make another release of this library.

[kravets-levko]

Yes, I took another look at these changes and totally agree with you. I'll revert all similar changes (private -> protected) and temporarily just suppress TS errors with @ts-expect-error

[kravets-levko]

Done 275bdbf

[kravets-levko]

For now I kept code that uses private fields and methods - this PR is already too big to add more refactoring. However, it turns out that TS allows to access private and protected fields using string indexing (obj['prop']) - TS still checks if property exists and keeps things type-safe, so I think it's still better than untyped code or with errors suppressed

[benc-db]

I'm approving but given how big an interface change we have here, primarily to remove type errors from tests, please get another reviewer before merge and consider my comment about refactoring in a way that introduces new types, rather than modifying the interface of existing types.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 93.54839% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 92.93%. Comparing base (3eed509) to head (6d2718b).

Files	Patch %	Lines
...nnection/auth/DatabricksOAuth/AuthorizationCode.ts	89.28%	2 Missing and 1 partial ⚠️
lib/connection/auth/DatabricksOAuth/index.ts	80.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #258      +/-   ##
==========================================
- Coverage   93.06%   92.93%   -0.13%     
==========================================
  Files          65       64       -1     
  Lines        1586     1572      -14     
  Branches      280      282       +2     
==========================================
- Hits         1476     1461      -15     
+ Misses         46       44       -2     
- Partials       64       67       +3     

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