codeintel: Call handleEnqueue from lsifserver proxy
Created by: efritz
This is step one into collapsing the precise-code-intel-api-server into the frontend. We expose the necessary logic to call the enqueue endpoint directly from the lsifserver "proxy".
The next step will be to do the same thing for the query endpoints from the LSIF resolvers.
These PRs are meant to create minimal diffs. A secondary clean-up effort to remove dead code and reduce call graph layers will be done after these lands.