[expr.prim.req.compound] Resolve conflicts in P1084R2 and P1141R2.

Replace /qualified-concept-name/ with /type-constraint/ in grammar
for /return-type-requirement/, and rewrite the new bullet for
/return-type-requirement/ added in P1084R2 to use the term
immediately-declared constraint introduced in P1141R2.

Author: Dawn Perchik

source/expressions.tex

@@ -2600,7 +2600,7 @@
 \begin{bnf}
 \nontermdef{return-type-requirement}\br
     trailing-return-type\br
-    \terminal{->} qualified-concept-name
+    \terminal{->} type-constraint
 \end{bnf}
 
 \pnum
@@ -2631,20 +2631,12 @@
     If conversion fails, the enclosing \grammarterm{requires-expression}
     is \tcode{false}.
   \item
-    If the \grammarterm{return-type-requirement} has a
-    a \grammarterm{qualified-concept-name}\iref{temp.param} of the form
-    \opt{\grammarterm{nested-name-specifier}} \grammarterm{concept-name},
-    the concept it denotes shall be satisfied with
-    \tcode{decltype((E))} as its sole argument.
-    If the \grammarterm{return-type-requirement} has a
-    a \grammarterm{qualified-concept-name} of the form
-    \opt{\grammarterm{nested-name-specifier}} \grammarterm{concept-name}
-    \tcode{<} \opt{\grammarterm{template-argument-list}} \tcode{>},
-    the concept it denotes shall be satisfied with
-    \tcode{decltype((E))} as its first argument and with
-    the elements, in the order listed, of
-    the \grammarterm{template-argument-list}
-    comprising the concept’s subsequent arguments.
+    If the \grammarterm{return-type-requirement}
+    is of the form \tcode{->} \grammarterm{type-constraint}, then
+    the contextually-determined type being constrained
+    is \tcode{decltype((E))}.
+    The immediately-declared constraint\iref(temp) of \tcode{decltype((E))}
+    shall be satisfied.
     \begin{note}
     Thus, constraints of the form
     \tcode{\{ E \} -> Concept;} or of the form