Customize module not found error message when on windows

[acoates-ms]

Summary

The error message that metro displays when it fails to resolve a module doesn't make sense on windows. The first option involves running watchman, which doesn't run on windows. And the last steps involves running some bash commands that don't exist on a default windows install.

So I'm changing what the message is when running on windows.

Test plan

[cpojer]

You'll need to update the tests too.

[cpojer]

@acoates-ms could you follow up on this one?