Bug 129214 [Field Assist] - Decorated Field attachments not centering images horizontally
DecoratedField is supposed to center decorations horizontally on each side. The current attachments are not doing so. Also consider whether grid would have been a better choice for internal implementation.
bundles/org.eclipse.jface/src/org/eclipse/jface/fieldassist/DecoratedField.java
/**
		 * Height of info hover arrow.
		 */
		private int hah = 10;
		/**
		 * Margin around info hover text.
		 */
		private int hm = 2;
		/**
		 * This info hover's shell.
		 */
		Shell hoverShell;
		/**
		 * The info hover text.
		 */
		String text = EMPTY;
		/**
		 * The region used to manage the shell shape
		 */
		Region region;
		/**
		 * Boolean indicating whether the last computed polygon location had an
		 * arrow on left. (true if left, false if right).
		 */
		boolean arrowOnLeft = true;
		/*
		 * Create a hover parented by the specified shell.
		 */
		Hover(Shell parent) {
			final Display display = parent.getDisplay();