Add iOS dynamic framework build and React Native op-sqlite docs

[gaodeng]

Summary

• add an optional iOS dynamic framework build script that produces an xcframework
• keep the existing iOS static library build as the default unless BUILD_IOS_DYNAMIC_FRAMEWORK is enabled
• document how to load simple from React Native with @op-engineering/op-sqlite

Testing

• ./build-ios.sh
• ./build-ios-dynamic.sh