dillon1000/react

Create a separate pass to prune non-reactive dependencies

The fact that InferReactiveIdentifiers is integrated directly into 
PropagateScopeDependencies has made the latter pretty tricky to debug at times. 
If a dependency is missing, we have to introspect and figure out if that's 
because it was somehow inferred as non-reactive. This PR creates a new 
PruneNonReactiveDependencies pass to separate out these phases.