pull symbols logic out of graphql

Created by: ijsnow

I'm working on refactoring search logic out of the graphql layer. I started this by pulling out symbols because:

1. we needed to do untangle symbol from graphql as part of untangling search from graphql.
2. it is a much smaller place to start than the whole search code path, so this will help others with visualizing the goal of the refactor.

Test plan: This is a refactor, so we're relying on existing tests.