Benchmark DFT-based fuzzing

//cc @kcc

I'd like to benchmark DFT-based fuzzing in the late Q2. Filing this issue now to outline the requirements, which hopefully could be addressed by then (if anything has to be addressed separately at all).

# What we need to benchmark

1. Vanilla libFuzzer (the most recent version on the day of starting the experiment)
2. (up to N) modified libFuzzer versions, with different heuristics / parameters tuned as per the work mentioned in https://github.com/google/oss-fuzz/issues/1632, https://github.com/google/oss-fuzz/issues/3398, and go/dft-cf design doc.

# Requirements

1. Different libFuzzer builds mentioned above are "fuzzers" for the experiment
2. Each benchmark should have saturated corpora
3. Each benchmark should have data flow traces for the given corpora
This is out of scope of the fuzzbench responsibilities, we just need to be able to include additional files in benchmarks. Prior to the experiment, we will build all benchmarks with DFSan and collect Data Flow Traces using dataflow driver.
4. Because of the points 2 and 3, we will use arbitrary fuzz targets from OSS-Fuzz