Let the new created embedded QLineEdit use the palette from QCombobox,
when calling [setEditable(true)]
Fixes: QTBUG-81533
Pick-to: 5.15
Change-Id: Ia406dd8122a348e185f0e94d027646b95eeaa76e
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>