AAPT2: Move comments and source into Value

Values are closely related to where they were defined, so
this information should live inside the Value.

This also enables comments to be attached to nested Values.

Change-Id: Ic7481b5a5f26d0ef248d638e2e29252f88154581
diff --git a/tools/aapt2/ResourceValues.cpp b/tools/aapt2/ResourceValues.cpp
index ecc5cd2..f312d75 100644
--- a/tools/aapt2/ResourceValues.cpp
+++ b/tools/aapt2/ResourceValues.cpp
@@ -15,11 +15,12 @@
  */
 
 #include "Resource.h"
-#include "flatten/ResourceTypeExtensions.h"
 #include "ResourceValues.h"
-#include "util/Util.h"
 #include "ValueVisitor.h"
 
+#include "util/Util.h"
+#include "flatten/ResourceTypeExtensions.h"
+
 #include <androidfw/ResourceTypes.h>
 #include <limits>
 
@@ -35,18 +36,10 @@
     visitor->visit(static_cast<Derived*>(this));
 }
 
-bool Value::isItem() const {
-    return false;
-}
-
 bool Value::isWeak() const {
     return false;
 }
 
-bool Item::isItem() const {
-    return true;
-}
-
 RawString::RawString(const StringPool::Ref& ref) : value(ref) {
 }