Support ClusterFuzz grouping for bug based benchmarking

[Oliver Chang]

Support ClusterFuzz grouping for bug based benchmarking

[jonathanmetzman]

This is high-priority work, dongge could you please take a look?

[Dongge Liu]

Yep, I am working on this.
For record purposes, this requires:

1. Expose ClusterFuzz's crash comparer.
2. Bump up the required version of CF dependency (to 2.6.0).
3. WIP replace FuzzBench's duplication algorithm with CF's crash comparer.

I am doing 2&3 in one PR.

[jonathanmetzman]

@Alan32Liu have you tested your implementation in an experiment?

[Dongge Liu]

@Alan32Liu have you tested your implementation in an experiment?

Yes: #1699 (comment)

I also started another 23-hour experiment yesterday and is waiting for its result.

[Dongge Liu]

I think this is completed : )