dillon1000/react

Make CompilerError.reason a static string

While running the latest Forget build on www I noticed that a lot of the 
bailouts were special-cases where we used interpolation in the error `reason` 
string to provide more context for debugging. This is a pretty cool result, 
because it means that we actually support nearly all the common syntax (at least 
based on a sample of the codebase). But it makes our tools for aggregating 
errors break down a bit. 

This PR adds a new, nullable `description` property to CompilerErrorDetail, and 
manually updates to ensure that we always pass a static `reason` and only use 
interpolation in the `description`. This will allow our aggregation tools to 
group by the reason.