Comment drift processing can timeout for extremely large pull requests

As part of comment drift processing, git diff is run to identify comments which need to be moved up or down, or removed entirely because they were made on lines which have been changed.

These git diff processes use the standard timeouts, meaning they get one minute of "idle" time (where they produce no output), and 2 minutes of total execution time.After two minutes, even if the processes are still running, they're canceled. For extremely large pull requests, whether modifying a large number of files, or making changes in large files, or both, two minutes may not be enough.

Comment drift should apply a separate timeout for its processes, to allow it to be configured without having to raise the global idle and execution timeouts for all processes. Additionally, there may be ways in which the git diff command being run could be optimized. As part of addressing this issue, such potential optimizations should be investigated. Comment drift is a frequently-performed operation, so any optimizations here could greatly benefit pull request-heavy instances.