dillon1000/react

Prune scopes whose deps always invalidate

Implements the optimization described in the previous PR: if we know that a 
scope's dependency will _always_ invalidate (it is not memoized and it is 
guaranteed to be a new object if the instruction executes, such as an array or 
object literal), then we can prune that scope. The invalidation is transitive: 
we track always-invalidating types from within scopes, and if their scope gets 
invalidated we prune downstream scope that depend on them. 

## Test Plan 

Tested via #2639 - see https://fburl.com/everpaste/3e3hjpjs. 91 files change 
output due to reactive scopes which would always invalidate due to always 
invalidating dependencies.