Discover VSTest and MSTest using VSWhere

[farlee2121]

Fake.DotNet.Testing.VSTest and Fake.DotNet.Testing.MSTest currently search for VSTest and MSTest respectively using hard-coded lists of possible paths. These paths are simply different versions of Visual Studio.

@robertpi previously did work to update these paths and partially move them to a VSWhere for locating Visual Studio installs.
The work was not merged. #2542

This PR rebases #2542 and further migrates VSTest discovery to use VSWhere.

This should reduce effort to keep Fake.DotNet.Testing.VSTest and Fake.DotNet.Testing.MSTest up to date as new versions of Visual Studio are released.

This PR will also fix the current issue where Fake.DotNet.Testing.VSTest cannot automatically discover VSTest with recent versions of Visual Studio.

Note that VSWhere only works for VisualStudio 2017+. We'll want to re-add hard-coded pre-2017 paths if we want to continue supporting those older versions of Visual Studio

@xperiandri

[github-actions]

Test Results

    9 files  ±0      9 suites  ±0   44m 13s ⏱️ - 2m 54s
  439 tests ±0    439 ✅ ±0  0 💤 ±0  0 ❌ ±0 
1 251 runs  ±0  1 251 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit ef20bf0. ± Comparison against base commit 6f2fc43.

[xperiandri]

@farlee2121 cool! Should I merge?

[farlee2121]

It should be ready to merge if you're also satisfied with it.