[dcl.init.ref] Clarify "related type"

"Related type" is not a term, "reference-related type" is clearer.

Author: frederick-vs-ja

source/declarations.tex

@@ -5721,9 +5721,10 @@
 const int& r3 = a;                  // error: cv-qualifier dropped
                                     // from result of conversion function
 double d2 = 1.0;
-double&& rrd2 = d2;                 // error: initializer is lvalue of related type
+double&& rrd2 = d2;                 // error: initializer is lvalue of reference-related type
 struct X { operator int&(); };
-int&& rri2 = X();                   // error: result of conversion function is lvalue of related type
+int&& rri2 = X();                   // error: result of conversion function is
+                                    // lvalue of reference-related type
 int i3 = 2;
 double&& rrd3 = i3;                 // \tcode{rrd3} refers to temporary with value \tcode{2.0}
 \end{codeblock}