In https://github.com/scylladb/scylladb/pull/13482 we renamed the reader permit states to more descriptive names. That PR however only covered only the states themselves and their usages, as well as the documentation in `docs/dev`.
This PR is a followup to said PR, completing the name changes: renaming all symbols, names, comments etc, so all is consistent and up-to-date.
Closes#13573
* github.com:scylladb/scylladb:
reader_concurrency_semaphore: misc updates w.r.t. recent permit state name changes
reader_concurrency_semaphore: update permit members w.r.t. recent permit state name changes
reader_concurrency_semaphore: update RAII state guard classes w.r.t. recent permit state name changes
reader_concurrency_semaphore: update API w.r.t. recent permit state name changes
reader_concurrency_semaphore: update stats w.r.t. recent permit state name changes
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