Write info messages to stdout

[nagulv]

Hi
Thanks a lot for this really useful tool. I recently tried to integrate our existing protoc compilation (that uses this plugin) into Visual Studio, and ran into the issue that Visual Studio assumes the tool failed since the "Writing mypy to " lines are written to stderr.

Could you accept this change to log Writing mypy to lines to stdout instead?

I'm not sure if there's a reason these are logged to stderr specifically, but I found this issue that was used to change mypy behaviour to not write all lines to stderr: Suggestion: write messages to stdout instead of stderr

[nipunn1313]

You can run the tool with --quiet if you'd like to hide the stderr.

Writing to stdout does not work, because protoc expects plugins to write the actual generated code to stdout.

You can tell (see the testsuites) that the proposed change (unfortunately) does not work.

Appreciate the idea. It does sound like the experience from visual studio is not ideal. I filed #537 to capture that pain point - and potentially make improvements in that area.