Support more than one native implementation of the same capability behind ONE JSI-facing HostObject/API surface, selected once at build time via a project config flag threaded through package.json, the Android build.gradle/CMakeLists.txt, and the iOS podspec. Use when the user wants to add a second (or third) native implementation of an existing capability — a vendored alternative library, a hardware-accelerated vs. software path, a paid/free SDK split — chosen once when the app is built, not switchable at runtime. Not for runtime-selectable behavior (that's just a regular constructor argument/method parameter) and not for a single implementation with optional features (t…
