Generalize CSVParsing so that it can be ran across all of String's
views, and add corresponding benchmarks.
Note: This does change the profile of the original benchmark, which
was an odd mixture of String and UTF16View.
The `legacyFactor` is 11 instead of 10, because of the wierd way the `repeatCount` translates to the workload size based on the number of lines in the `workloadBase`… it’s just so.
Those are benchmarks which took way too long or short to execute a single iteration or benchmarks which changed in time anyway because of previous fixes.
I renamed those benchmarks so that they are now treated as "new" benchmarks.
The first is copied from https://github.com/apple/swift/pull/13930's
contribution (with a minor bug fix applied). The second is an
adaptation that tries to avoid creating copies and operate using
indices directly.
