Format: Use QMap instead of QHash

As the items of QHash are arbitrarily ordered, so the same formats may generate
different formatKey

src/xlsx/xlsxformat.h

@@ -237,6 +237,7 @@ private:
     friend class RichStringPrivate;
     friend class SharedStrings;
     friend class ::FormatTest;
+    friend Q_XLSX_EXPORT QDebug operator<<(QDebug, const Format &f);
 
     bool fontIndexValid() const;
     int fontIndex() const;
@@ -274,6 +275,10 @@ private:
     QExplicitlySharedDataPointer<FormatPrivate> d;
 };
 
+#ifndef QT_NO_DEBUG_STREAM
+Q_XLSX_EXPORT QDebug operator<<(QDebug dbg, const Format &f);
+#endif
+
 QT_END_NAMESPACE_XLSX
 
 #endif // QXLSX_FORMAT_H