MenuButton: content is not centered by default

AFAIUnderstand, menu button has centered text and text+graphic combination.
But now it is left-aligned.

RULE ControlsAutomatedTestSuite/javafx/scene/control/test/labeled/MenuButtonsTest/setContentDisplayTest Exception org.jemmy.TimeoutExpiredException: State 'Control having expected image' has not been reached in ... milliseconds

RULE ControlsAutomatedTestSuite/javafx/scene/control/test/labeled/MenuButtonsTest/setEllipsisStringScreenshotTest Exception org.jemmy.TimeoutExpiredException: State 'Control having expected image' has not been reached in ... milliseconds

RULE ControlsAutomatedTestSuite/javafx/scene/control/test/labeled/MenuButtonsTest/setGraphicTextGapTest Exception org.jemmy.TimeoutExpiredException: State 'Control having expected image' has not been reached in ... milliseconds