Hook up existing Tests model data to the Test Explorer view

[d3r3kk]

Hook up existing test model data via the Tests data structure.

Implement the API from the prior task using actual tests data. Update the tree view to contain actual test model data, which can be pulled from the ITestCollectionStorageService`.

On the 'Discover Tests', 'Run Tests', or 'Run Specific Unit Test' command, update the Test TreeView and it's underlying data model.

NOTE: Icons for the test view items are specified by a URI. For the initial release, let's try and used whatever icons may be available from VS Code itself (find SVG files in the sources and make use of them).

NOTE: The Tests data structure might still have to be extended, or wrapped, or converted, to support all of the features we have in mind.

NOTE: I've added a task below where we augment direct integration with each of these user-issued commands, and have this just be in response to an update to the ITestCollectionStorageService - this is how it seems to work
today.

Update the current API used by the status bar - move to a publisher-subscriber model instead (we are currently tightly coupled). Don has a solution for this in mind that it quite trivial to implement, (similar to how we subscribe to changes in configSettings.ts).

This exists today in the file src/client/unittests/main.ts

There is already code today that displays results in the status bar. Use the exact API that it works with today.

• After tests have run
• After test discovery has run

Test for completion:

• Visual representation of data should be visible in the tree model view in a workspace at the time the workspace is loaded
• Issuing the command pallette command(s) and observing when:
  • A test file is added/removed/renamed
  • A test suite is added/removed/renamed
  • A test function is added/removed/renamed
  • A test function was successful but has started to failed
  • A test function was failing but has started to succeed
  • A test function was skipped but is now being run successfully
  • A test function was skipped but is now being run unsuccessfully
  • A test function was running but is now being skipped
  • All the above state changes for functions, applied to suites (can Python suites be skipped?)

[d3r3kk]

Turns out this is trivial to implement alongside #4273, will take this on as well. (The exploratory work is now complete, I need to handle some edge cases and create tests).