QPropertyBindingPrivate: fix -Wshadow in sourceLocation()

This is preparation of applying headercheck to private headers, too.

Renaming the returned value to `result` also obsoletes the need for
the ugly this-> qualification, otherwise easily misread for a compiler
hint to look up the name in a template base class (which here does not
exist).

Amends 4d579851c8.

Pick-to: 6.7 6.5 6.2
Task-number: QTBUG-126219
Change-Id: Ib683f3deec492acdd2bc61806a8b0467f18f0fe8
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
(cherry picked from commit 5cd3fec9f9a2bca8c27bdee6b185714983b5d11e)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/kernel/qproperty_p.h

@@ -385,11 +385,11 @@ public:
     QPropertyBindingSourceLocation sourceLocation() const
     {
         if (!hasCustomVTable())
-            return this->location;
-        QPropertyBindingSourceLocation location;
+            return location;
+        QPropertyBindingSourceLocation result;
         constexpr auto msg = "Custom location";
-        location.fileName = msg;
-        return location;
+        result.fileName = msg;
+        return result;
     }
     QPropertyBindingError bindingError() const { return m_error; }
     QMetaType valueMetaType() const { return metaType; }