Deduce KEY and ALLOCATOR from an initializer_list constructor.
Declared in <bslstl_set.h>
template<
class KEY,
class ALLOCATOR>
requires bsl::IsStdAllocator_v<ALLOCATOR>
set<KEY, std::less<KEY>, ALLOCATOR>(
std::initializer_list<KEY>,
ALLOCATOR) -> set<KEY, std::less<KEY>, ALLOCATOR>;