Clarify behavior of setData in QListWidget, QTableWidget, and QTreeWidget

setData()'s default implementation for QListWidget, QTableWidget, and
QTreeWidget treats Qt::EditRole and Qt::DisplayRole as referring to the
same data. Used the same sentence from QStandardItem::setData for
consistency.

Task-number: QTBUG-11549
Change-Id: I41d06bdaaa8e7d4a86e24147b3d8222ad7823a6c
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Reviewed-by: Andy Shaw <andy.shaw@qt.io>

src/widgets/itemviews/qlistwidget.cpp

@@ -690,6 +690,9 @@ QListWidgetItem *QListWidgetItem::clone() const
     Sets the data for a given \a role to the given \a value. Reimplement this
     function if you need extra roles or special behavior for certain roles.
 
+    \note The default implementation treats Qt::EditRole and Qt::DisplayRole as
+    referring to the same data.
+
     \sa Qt::ItemDataRole, data()
 */
 void QListWidgetItem::setData(int role, const QVariant &value)

src/widgets/itemviews/qtablewidget.cpp

@@ -1365,6 +1365,9 @@ QTableWidgetItem *QTableWidgetItem::clone() const
 /*!
     Sets the item's data for the given \a role to the specified \a value.
 
+    \note The default implementation treats Qt::EditRole and Qt::DisplayRole as
+    referring to the same data.
+
     \sa Qt::ItemDataRole, data()
 */
 void QTableWidgetItem::setData(int role, const QVariant &value)

src/widgets/itemviews/qtreewidget.cpp

@@ -1699,6 +1699,9 @@ Qt::ItemFlags QTreeWidgetItem::flags() const
 
     The \a role describes the type of data specified by \a value, and is defined by
     the Qt::ItemDataRole enum.
+
+    \note The default implementation treats Qt::EditRole and Qt::DisplayRole as
+    referring to the same data.
 */
 void QTreeWidgetItem::setData(int column, int role, const QVariant &value)
 {