LSIF: conversion: allow correlation without pruning

Created by: slimsag

I am working on a better, more extensive test suite for the Sourcegraph documentation extension to LSIF. Specifically, I am making a better version of what is in the lsif-go indexer currently (generating static markdown files from the LSIF data for snapshot testing.)

I would like to use lib/codeintel/lsif/conversion directly because it does a lot of the annoying data correlation for me. But in the context of snapshot testing, data pruning is not relevant (and could hide useful information) so this commit makes it optional.

Signed-off-by: Stephen Gutekanst [email protected]