[Serialization] Always print the name associated to an XRefError

Printing the name will help in the case of xrefs for an extension member
and more. This will create errors messages like this in the case of a
module with an extension not being loaded:
```
x.	*** DESERIALIZATION FAILURE ***
module 'SomeModule' with full misc version ...
module with extension is not loaded (MyExtensionModule)
Cross-reference to module 'TypesOriginalModule'
... TypeBeingExtended
```

rdar://91316948

Author: xymus

lib/Serialization/Deserialization.cpp

@@ -1891,7 +1891,7 @@ ModuleFile::resolveCrossReference(ModuleID MID, uint32_t pathLen) {
       XRefExtensionPathPieceLayout::readRecord(scratch, ownerID, rawGenericSig);
       M = getModule(ownerID);
       if (!M) {
-        return llvm::make_error<XRefError>("module is not loaded",
+        return llvm::make_error<XRefError>("module with extension is not loaded",
                                            pathTrace, getIdentifier(ownerID));
       }
       pathTrace.addExtension(M);

lib/Serialization/DeserializationErrors.h

@@ -282,7 +282,7 @@ class XRefError : public llvm::ErrorInfo<XRefError, DeclDeserializationError> {
   }
 
   void log(raw_ostream &OS) const override {
-    OS << message << "\n";
+    OS << message << " (" << name << ")\n";
     path.print(OS);
 
     if (!notes.empty()) {