Gets the placement of the label.
Valid values in MXML are: right, left, bottom, center, and top.
In ActionScript, you can use use the following constants to set this property: ProgressBarLabelPlacement.RIGHT, ProgressBarLabelPlacement.LEFT, ProgressBarLabelPlacement.BOTTOM, ProgressBarLabelPlacement.CENTER, and ProgressBarLabelPlacement.TOP.
The default value is ProgressBarLabelPlacement.BOTTOM.