[CodeCompletion] Deduplicate the two isMemberCompletion functions in ParseExpr.cpp and ParseDecl.cpp

Also:
- propagate the Solution -> Result rename to Solution parameter of deliverDotExprResults
- fixup header comment in CodeCompletionTypeChecking.h

lib/Parse/Parser.cpp

@@ -1185,6 +1185,34 @@ Parser::getStringLiteralIfNotInterpolated(SourceLoc Loc,
                                                Segments.front().Length));
 }
 
+bool Parser::
+shouldSuppressSingleExpressionBodyTransform(ParserStatus Status,
+                                            MutableArrayRef<ASTNode> BodyElems) {
+  if (BodyElems.size() != 1)
+    return true;
+
+  if (!Status.hasCodeCompletion())
+    return false;
+
+  struct HasMemberCompletion: public ASTWalker {
+    bool Value = false;
+    std::pair<bool, Expr *> walkToExprPre(Expr *E) override {
+      if (auto *CCE = dyn_cast<CodeCompletionExpr>(E)) {
+        // If it has a base expression this is member completion, which is
+        // performed using the new solver-based mechanism, so it's ok to go
+        // ahead with the transform (and necessary to pick up the correct
+        // expected type).
+        Value = CCE->getBase();
+        return {false, nullptr};
+      }
+      return {true, E};
+    }
+  };
+  HasMemberCompletion Check;
+  BodyElems.front().walk(Check);
+  return !Check.Value;
+}
+
 struct ParserUnit::Implementation {
   std::shared_ptr<SyntaxParseActions> SPActions;
   LangOptions LangOpts;