Add a NAPI-JSI build to pre-test Babylon React Native

[rgerd]

We just need to fill in the gaps to implement an AppRuntimeJSI and add some CMake to consume the proper headers and libraries from the v8-jsi project.

This will help us catch issues in the future like these:
#822
#805

And could help diagnose this issue:
https://github.com/BabylonJS/BabylonReactNative/issues/257