Previously, some fuzzers were generating an excessive amount of debug
logging. This change explicitly disables debug logging for all fuzzers.
This allows higher test throughput and makes the logs easier to read
when fuzzing locally.
We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
