Add back QWheelEvent position() and globalPosition() docs

Change 7d29807296 removed the docs for
the obsolete pos() and globalPos() accessors, but the text should have
been reused to document their replacements.

Change-Id: If4d64e0f07666a99d9a0a4f0de9fca42d3acf0f8
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>

src/gui/kernel/qevent.cpp

@@ -931,6 +931,30 @@ QWheelEvent::~QWheelEvent()
     \endlist
 */
 
+/*!
+    \fn QPoint QWheelEvent::position() const
+
+    Returns the position of the mouse cursor relative to the widget
+    that received the event.
+
+    If you move your widgets around in response to mouse events,
+    use globalPosition() instead of this function.
+
+    \sa globalPosition()
+*/
+
+/*!
+    \fn QPoint QWheelEvent::globalPosition() const
+
+    Returns the global position of the mouse pointer \e{at the time
+    of the event}. This is important on asynchronous window systems
+    such as X11; whenever you move your widgets around in response to
+    mouse events, globalPosition() can differ a lot from the current
+    cursor position returned by QCursor::pos().
+
+    \sa position()
+*/
+
 #if QT_DEPRECATED_SINCE(5, 15)
 /*!
     \fn int QWheelEvent::delta() const