Update icons and tooltip in test explorer indicating status of test files/suites

[qubitron]

Per spec:

Hover should optionally show number of pass/fail:

[DonJayamanne]

• When tests have not run what's the icon against the file, folder, suite, function?
  • Green check mark for all successful tests
  • If any test fails, then parent fails
  • When status = Idle or Unknown, then display a "Not Run" icon
  • Similarly, tooltips would be a summary of all child nodes
• What happens when a test is skipped?
  • Display not run icon

[DonJayamanne]

File to modify:

• src/client/unittests/explorer/testTreeViewItem.ts
• Create new tooltip getter to provide tooltip based on data
• Existing iconPath getter to provide icon based on data

[qubitron]

@DonJayamanne we should have a "not run" icon that is the same across all levels, if a test is skipped (how?) then it would be the same as not running it.