Benchmarks build_runner against synthetic codebases applying real generators: built_value, freezed, json_serializable or mockito.

Example usage:

# Benchmark `build_runner` from pub.
dart run _benchmark \
    --generator=built_value \
    benchmark

# Benchmark a local version of `build_runner`.
dart run _benchmark \
    --generator=built_value \
    --build-repo-path=$PWD/.. \
    benchmark