Turn on Text Buffer unit tests in Azure DevOps CI build

[metathinker]

This small PR renames the text buffer unit test binary file from TextBuffer.UnitTests.dll to TextBuffer.Unit.Tests.dll, with a dot between "Unit" and "Tests". As per the discussion for issue #854, this should be enough to get those tests running in CI.

Detailed Description of the Pull Request / Additional comments

Though it was not strictly necessary, I also renamed the Visual Studio project for TextBuffer.Unit.Tests.dll and its .vcxproj project file.

I also noticed that the 2 tools\ folder commands used to run tests were inconsistent with each other. That is, the PowerShell Invoke-OpenConsoleTests cmdlet was missing some tests run by the {runut,runft,runuia}.cmd batch files (though not the same tests that Azure CI was missing!). So I took the liberty of updating the cmdlet to run those missing tests.

I did not touch the files used in the Windows OS build and test system (the sources file and testmd.definition file). I didn't think this was necessary because the DLLs built by the sources and .vcxproj files are already inconsistent in filename, for this DLL as well as some other binaries built in this repo.

PR Checklist

• Closes Check status of TextBuffer Unit Tests in CI #854
• CLA signed - N/A; I work for Microsoft
• Tests added/passed - manually verified that the Buffer unit tests now run and pass in CI build: https://github.com/microsoft/terminal/pull/1057/checks?check_run_id=138408795
• Requires documentation to be updated - N/A; no doc changes needed
• I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan.

[miniksa]

Beautiful. Thank you very much.

[DHowett-MSFT]

Yay! Thanks!