[lib] Remove friend class X (#6427)

Friendship between library classes is considered an implementation detail.

Author: frederick-vs-ja

source/containers.tex

@@ -9266,7 +9266,6 @@
 
     // bit reference
     class @\libmember{reference}{vector<bool>}@ {
-      friend class vector;
       constexpr reference() noexcept;
 
     public:
@@ -10380,7 +10379,6 @@
     using insert_return_type     = @\placeholdernc{insert-return-type}@<iterator, node_type>;
 
     class value_compare {
-      friend class map;
     protected:
       Compare comp;
       value_compare(Compare c) : comp(c) {}
@@ -11117,7 +11115,6 @@
     using node_type              = @\unspec@;
 
     class value_compare {
-      friend class multimap;
     protected:
       Compare comp;
       value_compare(Compare c) : comp(c) { }

source/iostreams.tex

@@ -16096,7 +16096,6 @@
 
   private:
     filesystem::path pathobject;        // \expos
-    friend class directory_iterator;    // \expos
   };
 }
 \end{codeblock}
@@ -16115,10 +16114,7 @@
 
 \pnum
 \begin{note}
-For purposes of exposition,
-class \tcode{directory_iterator}\iref{fs.class.directory.iterator}
-is shown above as a friend of class \tcode{directory_entry}.
-Friendship allows the \tcode{directory_iterator} implementation to cache
+\tcode{directory_iterator} can cache
 already available attribute values
 directly into a \tcode{directory_entry} object
 without the cost of an unneeded call to \tcode{refresh()}.
@@ -16620,8 +16616,6 @@
 any \tcode{directory_entry} \tcode{refresh} function.
 \begin{note}
 The exact mechanism for storing cached attribute values is not exposed to users.
-For exposition, class \tcode{directory_iterator} is shown in \ref{fs.class.directory.entry}
-as a friend of class \tcode{directory_entry}.
 \end{note}
 
 \pnum

source/utilities.tex

@@ -9799,7 +9799,6 @@
   public:
     // bit reference
     class reference {
-      friend class bitset;
       constexpr reference() noexcept;
 
     public:
@@ -18605,8 +18604,6 @@
 
     template<class T> explicit handle(T& val) noexcept;         // \expos
 
-    friend class basic_format_arg<Context>;                     // \expos
-
   public:
     void format(basic_format_parse_context<char_type>&, Context& ctx) const;
   };