queue: add back template requirement for element type to be nothrow move-constructible
queue: add back template requirement for element type to be nothrow move-constructible

It was reverted in b1cdb8ed24bf0a09f63173dd191869a5b9f4b4ed
due to clang 12 errors.

This change re-adds the template requriement to the
class definition, and adds the require concept also
to all out-of-line template redeclarations.

Test: unit(dev) built with clang version 12.0.1 -std=c++20

Signed-off-by: Benny Halevy <23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>
Message-Id: <20211019135731.1702541-1-23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>

avikivity/seastar,syuu1228/seastar,scylladb/seastar,avikivity/seastar,avikivity/seastar,syuu1228/seastar,syuu1228/seastar,scylladb/seastar,scylladb/seastar