in af2553e8, we added formatters for cdc::image_mode and
cdc::delta_mode. but in that change, we failed to qualify `string_view`
with `std::` prefix. even it compiles, it depends on a `using
std::string_view` or a more error-prone `using namespace std`.
neither of which shold be relied on. so, in this change, we
add the `std::` prefix to `string_view`.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#17459
8afdc503b8