Shadow styles are deprecated

[Downchuck]

shadow*" style props are deprecated. Use "boxShadow

See: necolas/react-native-web#2620

Triggered by components/BaseToast.styles.js

[huytdps13400]

This is now covered by #601. The fix uses a web-only boxShadow in BaseToast.styles while keeping the existing native shadow props and Android elevation. It also adds platform-isolated regressions proving that the web style contains none of shadowOffset, shadowOpacity, or shadowRadius, so the import-time React Native Web warning is no longer triggered. The full quality gate passes with 85 tests and 100% coverage.