QLineEdit: disable cursor blinking on hide

QLineEdit activates the blinking cursor timer when it's shown,
but never deactivates it, resulting in constant wakeups even for
hidden line edits.

Note that this is a workaround. Qt is supposed to send a focus out
event to line edits that get hidden. In some corner cases, it
doesn't, and only a hide event is sent.

Change-Id: Ic0645512051466ca9b1e84c54cef34c22287338b
Task-number: QTBUG-52021
Pick-to: 6.7 6.6 6.5
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

src/widgets/widgets/qlineedit.cpp

@@ -1462,6 +1462,8 @@ bool QLineEdit::event(QEvent * e)
                 || style()->styleHint(QStyle::SH_BlinkCursorWhenTextSelected, &opt, this))
                 d->setCursorVisible(true);
         }
+    } else if (e->type() == QEvent::Hide) {
+        d->control->setBlinkingCursorEnabled(false);
 #if QT_CONFIG(action)
     } else if (e->type() == QEvent::ActionRemoved) {
         d->removeAction(static_cast<QActionEvent *>(e)->action());