Improve test discovery experience

[GeorchW]

This PR is a collection of multiple QOL changes to make test discovery more intuitive:

• Add a hint to set testProjectPath when no tests are found. This includes a link to the settings:
  
  (Sadly, the markdown does not seem to support code blocks for the setting.)
• Add examples to the testProjectPath setting that include globs:
  
• Rerun the glob when pressing "Refresh" (it's nasty when you rename some files, press refresh and the test explorer doesn't update)
• Rename the output log to ".NET Test Explorer" (the name "Test Explorer" is already used by other extensions on my setup, leading to confusion that I'm probably not alone with)

I'd say that this fixes #217.

[stefanforsberg]

You are on 🔥!

Love all these, thanks a bunch!

[GeorchW]

... sorry, but did you forget to merge?

[stefanforsberg]

No :p