LSIF: switch to ID-based filenames
Created by: chrismwendt
This is one more piece necessary for multi-lang/project support where we'll need to store multiple dumps per repo@commit.
Prior to this change, each individual SQLite DB was named based on the repo@commit. It would be rather awkward to keep shoving metadata into the filenames to ensure they're unique and don't conflict with each other.
After this change, each individual SQLite DB will be named based on the associated primary key in the lsif_dumps
table. That lets us add metadata in Postgres without changing the filenames.
Test plan: manually checked that files get renamed
RFC 24: LSIF for multi-project repositories
Depends on https://github.com/sourcegraph/sourcegraph/pull/5947