[libc++][NFC] Replace typedefs with using aliases in <string> (#126070)

Author: philnik777

libcxx/include/string

@@ -764,18 +764,18 @@ struct __padding<0> {};
 template <class _CharT, class _Traits, class _Allocator>
 class basic_string {
 public:
-  typedef basic_string __self;
-  typedef basic_string_view<_CharT, _Traits> __self_view;
-  typedef _Traits traits_type;
-  typedef _CharT value_type;
-  typedef _Allocator allocator_type;
-  typedef allocator_traits<allocator_type> __alloc_traits;
-  typedef typename __alloc_traits::size_type size_type;
-  typedef typename __alloc_traits::difference_type difference_type;
-  typedef value_type& reference;
-  typedef const value_type& const_reference;
-  typedef typename __alloc_traits::pointer pointer;
-  typedef typename __alloc_traits::const_pointer const_pointer;
+  using __self _LIBCPP_NODEBUG         = basic_string;
+  using __self_view _LIBCPP_NODEBUG    = basic_string_view<_CharT, _Traits>;
+  using traits_type                    = _Traits;
+  using value_type                     = _CharT;
+  using allocator_type                 = _Allocator;
+  using __alloc_traits _LIBCPP_NODEBUG = allocator_traits<allocator_type>;
+  using size_type                      = typename __alloc_traits::size_type;
+  using difference_type                = typename __alloc_traits::difference_type;
+  using reference                      = value_type&;
+  using const_reference                = const value_type&;
+  using pointer                        = typename __alloc_traits::pointer;
+  using const_pointer                  = typename __alloc_traits::const_pointer;
 
   // A basic_string contains the following members which may be trivially relocatable:
   // - pointer: is currently assumed to be trivially relocatable, but is still checked in case that changes
@@ -838,14 +838,14 @@ public:
   // Users might provide custom allocators, and prior to C++20 we have no existing way to detect whether the allocator's
   // pointer type is contiguous (though it has to be by the Standard). Using the wrapper type ensures the iterator is
   // considered contiguous.
-  typedef __bounded_iter<__wrap_iter<pointer> > iterator;
-  typedef __bounded_iter<__wrap_iter<const_pointer> > const_iterator;
+  using iterator       = __bounded_iter<__wrap_iter<pointer> >;
+  using const_iterator = __bounded_iter<__wrap_iter<const_pointer> >;
 #  else
-  typedef __wrap_iter<pointer> iterator;
-  typedef __wrap_iter<const_pointer> const_iterator;
+  using iterator       = __wrap_iter<pointer>;
+  using const_iterator = __wrap_iter<const_pointer>;
 #  endif
-  typedef std::reverse_iterator<iterator> reverse_iterator;
-  typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
+  using reverse_iterator       = std::reverse_iterator<iterator>;
+  using const_reverse_iterator = std::reverse_iterator<const_iterator>;
 
 private:
   static_assert(CHAR_BIT == 8, "This implementation assumes that one byte contains 8 bits");