Spell out the move rationale at every handle_value(std::move) site

The comment explaining why the value is moved sat only on
json_sax_dom_parser::string(), and the callback parser's string() pointed
at it with "see json_sax_dom_parser::string()". That reference cannot be
searched for - the function is declared as `bool string(string_t& val)`
inside the class, so the qualified name appears nowhere - and the two
binary() overloads, which have always moved, carried no explanation at all.

Put the same comment on all four sites and name json_sax, which is
greppable, instead of a member that is not.

Comment-only; no generated code changes.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

include/nlohmann/detail/input/json_sax.hpp

@@ -222,14 +222,16 @@ class json_sax_dom_parser
 
     bool string(string_t& val)
     {
-        // the interface allows moving the value (see json_sax::string), which
+        // json_sax documents that the passed value may be moved from,
-        // hands the lexer's buffer to the new value instead of copying it
+        // so hand the buffer over instead of copying it
         handle_value(std::move(val));
         return true;
     }
 
     bool binary(binary_t& val)
     {
+        // json_sax documents that the passed value may be moved from,
+        // so hand the buffer over instead of copying it
         handle_value(std::move(val));
         return true;
     }
@@ -534,13 +536,16 @@ class json_sax_dom_callback_parser
 
     bool string(string_t& val)
     {
-        // see json_sax_dom_parser::string()
+        // json_sax documents that the passed value may be moved from,
+        // so hand the buffer over instead of copying it
         handle_value(std::move(val));
         return true;
     }
 
     bool binary(binary_t& val)
     {
+        // json_sax documents that the passed value may be moved from,
+        // so hand the buffer over instead of copying it
         handle_value(std::move(val));
         return true;
     }

single_include/nlohmann/json.hpp

@@ -10935,14 +10935,16 @@ class json_sax_dom_parser
 
     bool string(string_t& val)
     {
-        // the interface allows moving the value (see json_sax::string), which
+        // json_sax documents that the passed value may be moved from,
-        // hands the lexer's buffer to the new value instead of copying it
+        // so hand the buffer over instead of copying it
         handle_value(std::move(val));
         return true;
     }
 
     bool binary(binary_t& val)
     {
+        // json_sax documents that the passed value may be moved from,
+        // so hand the buffer over instead of copying it
         handle_value(std::move(val));
         return true;
     }
@@ -11247,13 +11249,16 @@ class json_sax_dom_callback_parser
 
     bool string(string_t& val)
     {
-        // see json_sax_dom_parser::string()
+        // json_sax documents that the passed value may be moved from,
+        // so hand the buffer over instead of copying it
         handle_value(std::move(val));
         return true;
     }
 
     bool binary(binary_t& val)
     {
+        // json_sax documents that the passed value may be moved from,
+        // so hand the buffer over instead of copying it
         handle_value(std::move(val));
         return true;
     }