QXmlStreamPrivateTagStack: don't fail on more than 2Gi chars in the tag stack

QXmlStreamPrivateTagStack holds the string data in a single large
QString, which, on 64-bit platforms, can hold more than INT_MAX
characters' worth of data. However, the code managing this QString
still used int variables instead of qsizetype, making failure for such
large tag string data all but inevitable, even though I didn't go to
the length of actually constructing a failing test case.

Fix by using qsizetype instead of int where required.

Fixes: QTBUG-102467
Pick-to: 6.3 6.2
Change-Id: I50b7e194e43f3c7dce69c6e1fd4682fc517dd7d6
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/serialization/qxmlstream_p.h

@@ -191,7 +191,7 @@ public:
         XmlStringRef name;
         XmlStringRef qualifiedName;
         NamespaceDeclaration namespaceDeclaration;
-        int tagStackStringStorageSize;
+        qsizetype tagStackStringStorageSize;
         qsizetype namespaceDeclarationsSize;
     };
 
@@ -199,14 +199,14 @@ public:
     QXmlStreamPrivateTagStack();
     QXmlStreamSimpleStack<NamespaceDeclaration> namespaceDeclarations;
     QString tagStackStringStorage;
-    int tagStackStringStorageSize;
-    int initialTagStackStringStorageSize;
+    qsizetype tagStackStringStorageSize;
+    qsizetype initialTagStackStringStorageSize;
     bool tagsDone;
 
     XmlStringRef addToStringStorage(QStringView s)
     {
-        int pos = tagStackStringStorageSize;
-        int sz = s.size();
+        qsizetype pos = tagStackStringStorageSize;
+        qsizetype sz = s.size();
         if (pos != tagStackStringStorage.size())
             tagStackStringStorage.resize(pos);
         tagStackStringStorage.append(s.data(), sz);