Emit returnPressed() signal for the lineEdit embedded in QDateTimeEdit

f78842abe429dc9b42fd15dc8e9e842ab72dcf2b added the emission of the
signal in QAbstractLineEdit::keyPressEvent(). This patch also emits
it for QDateTimeEdit.

Fixes: QTBUG-73725
Change-Id: I66d577f5d4b60ad57987b26e7a1c1f20fad47782
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

src/widgets/widgets/qdatetimeedit.cpp

@@ -1092,6 +1092,7 @@ void QDateTimeEdit::keyPressEvent(QKeyEvent *event)
         d->setSelected(d->currentSectionIndex, true);
         event->ignore();
         emit editingFinished();
+        emit d->edit->returnPressed();
         return;
     default:
 #ifdef QT_KEYPAD_NAVIGATION