Unify benchmark names

[zbraniecki]

Now that we did more work around Plurals benchmarks I have a framework to work with documented here: https://github.com/unicode-org/icu4x/wiki/Benchmarking

I'd like to take all benchmarks and separate overview from detailed benchmarks for 0.1, even if we don't separate ones run by default from ones behind bench feature.

The goal is so that when you run cargo bench overview you get only a subset of benchmarks that are giving a high level overview and this is what we'll use in CI.