Fixed move constructor and operator of
`readers_cache::range_lock_holder`. Previously moving the
`range_lock_holder` would result in lock being released.

Signed-off-by: Michal Maslanka <michal@redpanda.com>

Fixed condition checking if range is locked. Incorrect check resulted in
situations in which log truncation was blocked by pending readers.

Log truncation is multi step process that ends with grabbing necessary
segments write logs and data deletion. In order for truncation to grab
the write lock all readers which own read lock units from range being
truncated must be evicted from `readers_cache`. Since log truncation
contains multiple scheduling points it may interleave with another fiber
creating a reader for log that is currently being truncated. This reader
MUST not be cached as truncation would need to wait for it to be
evicted. Additionally no new readers can be created as truncation
related write lock request is waiting in the `read_write_lock`
underlying semaphore waiters queue.

In order to prevent readers requesting truncated range from being cached
readers cache maintain list of locked ranges i.e. ranges for which
readers can not be cached.

Previously an incorrect condition checking if reader belongs to locked
range allow it to be cached preventing the `truncate` action to
continue. This stopped all other writes and truncation for 60 seconds,
after this duration the reader was evicted from the cache, its lease was
released and trucation was able to finish.

Fixed incorrect condition checking if reader is within the locked
range.

Fixes: redpanda-data#5510

Signed-off-by: Michal Maslanka <michal@redpanda.com>

Signed-off-by: Michal Maslanka <michal@redpanda.com>