Enable test timeout dump collection

[marcpopMSFT]

I do not know the history on why we launch our tests with dotnet-exec. We may hae to change the arguments to match the above commands that we use on netfx (and simplify to just use one).

I'm starting with this just to see if it'll work.

Also open question is where will the dump end up.

[marcpopMSFT]

This doesn't appear to work on non-windows:
The test source file "/private/tmp/helix/working/AB8E0979/w/B5F809E7/e/trx" provided was not found.

And any test that requires msbuildforwardingapp doesn't appear to work correctly within the dotnet test execution.

Applying a fix for the path variable as it was adding quotes that weren't meant to be there.

[marcpopMSFT]

@dsplaisted some of the other failures doing this are because we end up getting the host from the environment but that's now testhost.exe: https://github.com/dotnet/sdk/blob/main/src/Cli/Microsoft.DotNet.Cli.Utils/ForwardingAppImplementation.cs#L99

Is there a better way to find dotnet.exe that we already have in our test infrastructure?