Added TestEventListener

[ManickaP]

Allows logging of specific event sources into test output. Useful for test debugging. Usage:

private TestEventListener _listener;

public MsQuicQuicStreamConformanceTests(ITestOutputHelper output)
{
    _output = output;
    _listener = new TestEventListener(_output, "Private.InternalDiagnostics.System.Net.Quic");
}
protected override void Dispose(bool disposing)
{
    _listener.Dispose();
    base.Dispose(disposing);
}

[ghost]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[wfurt]

LGTM.
It may be with off adding at least some hook as example.
We have other places (DOTNET_TEST_NET_SECURITY_FORCE_SOCKET_STREAMS & DOTNET_TEST_HTTP2_FORCEUNENCRYPTEDLOOPBACK) where hooks like this are enable via environmental variables.

[CarnaViire]

Thanks!