Default the Windows standalone app to ASIO

[sdatkinson]

Summary

• default new Windows standalone settings to ASIO instead of DirectSound
• update the pinned iPlug2 host so applications can select a platform-specific default without changing other standalone apps
• continue honoring explicit driver values already present in settings.ini

Dependency

• Allow apps to choose the default audio driver iPlug2#17 adds the configurable standalone-driver default used here

Tests

• confirmed preprocessing with APP_API and _WIN32 defines APP_DEFAULT_AUDIO_DRIVER as 1
• confirmed macOS preprocessing does not override the framework default
• xcodebuild -workspace NeuralAmpModeler/NeuralAmpModeler.xcworkspace -scheme macOS-APP -configuration Debug -derivedDataPath /tmp/nam-issue-655-derived CODE_SIGNING_ALLOWED=NO build
• GitHub Actions Build Native: Windows and macOS jobs passed

Resolves #655