Fix standalone audio device-pair validation

[sdatkinson]

Summary

• update the iPlug2 submodule to merged Validate standalone audio device pairs before opening streams iPlug2#19
• validate persisted audio devices by direction and required channel capacity before opening a standalone stream
• require one duplex device for ASIO while retaining DirectSound as the Windows default
• fall back to compatible devices and persist the fallback only after audio starts successfully

Tests

• MSBuild.exe NeuralAmpModeler/NeuralAmpModeler.sln /m /t:NeuralAmpModeler-app /p:Configuration=Release /p:Platform=x64 /verbosity:minimal

Resolves #655