Draft modification to redirect logs to test output

[harishsk]

Currently when running tests the channel output doesn't appear in the test logs. This is a draft change to enable that functionality in order to get better logging to debug tests better.

There are two changes here.
The first is a simple adds a handler for MLContext's Log event and logs the message to test output. The second adds a TextWriter derived class to ConsoleEnvironment that makes ConsoleEnvironment also log to the test console if the code is running a test environment.

I am putting this PR up for review for two purposes.

The first is for general verification of the code and concept. And while the code reviews are in progress I am also using this to try and debug the failure in BinaryClassifierSymSgdTest in the CI builds.

[justinormont]

Related issues on having an output verbosity level besides zero & firehose:

• Log Verbosity Handling in MLContext #3235
• Stuck on evaluate #3920

[harishsk]

I understand the issue about the all or nothing logs. It would be good to add additional params to control the verbosity but that will impact the public API. I want the full logs right now to debug test failures. Can we defer the issue of adding additional control params?

[justinormont]

Can we defer the issue of adding additional control params?

Oh certainly. I was hoping/dreaming that both the unit test and user level logging could be solved in the same way.

[harishsk]

I have added additional params to LoggingEventArgs

[sharwell]

Can we not log to a file that gets attached as a build artifact?

[harishsk]

I think it is better in the default test log. It gives more flexibility that if I am running a single test locally on the console, I can see the output on the console or redirect to a file as I see fit. And on the build server, it gets logged to a file anyway. It it still a file whether it is in the artifacts or the default log file.

[frank-dong-ms-zz]