Display results per node in test explorer (and maybe in console)

[IgorFedchenko]

As described in this section of TestAdapter how-to it is possible to show several results per one spec. Example is how xunit shows results for [Theory] marked tests.

Might be a good idea to display each node's result in such way, and global spec result in parent node.

[IgorFedchenko]

After merging of #18 each node's spec is reported as separate test result. So need to group that results into single TestCase to make them children on one node in test explorer (and maybe they will be grouped in dotnet test output as well).

[Aaronontheweb]

I know our .trx formatter used to support this on the back-end:

Link to test run (retained)

Now when we have an MNTR failure inside Azure DevOps it looks like this instead:

Link to test run (retained)

We've lost the "tree" output that we used to have - in the past it was our customer TrxExporter that handled this. The VSTestAdapter output should handle it now, so we likely need to change how we're structuring results in order to solve both problems.