AST: Requestify lookup of protocol referenced by ImplementsAttr

Direct lookup relied in primary file checking to have filled in the
protocol type stored in the ImplementsAttr. This was already wrong
with multi-file test cases in non-WMO mode, and crashed in the
ASTPrinter if printing a declaration in a non-primary file.

I don't have a standalone test case that is independent of my
upcoming ASTPrinter changes, but this is a nice cleanup regardless.

lib/Sema/DerivedConformanceEquatableHashable.cpp

@@ -417,16 +417,12 @@ deriveEquatable_eq(
   // Add the @_implements(Equatable, ==(_:_:)) attribute
   if (generatedIdentifier != C.Id_EqualsOperator) {
     auto equatableProto = C.getProtocol(KnownProtocolKind::Equatable);
-    auto equatableTy = equatableProto->getDeclaredInterfaceType();
-    auto equatableTyExpr = TypeExpr::createImplicit(equatableTy, C);
     SmallVector<Identifier, 2> argumentLabels = { Identifier(), Identifier() };
     auto equalsDeclName = DeclName(C, DeclBaseName(C.Id_EqualsOperator),
                                    argumentLabels);
-    eqDecl->getAttrs().add(new (C) ImplementsAttr(SourceLoc(),
-                                                  SourceRange(),
-                                                  equatableTyExpr,
-                                                  equalsDeclName,
-                                                  DeclNameLoc()));
+    eqDecl->getAttrs().add(ImplementsAttr::create(parentDC,
+                                                  equatableProto,
+                                                  equalsDeclName));
   }
 
   if (!C.getEqualIntDecl()) {