Bug 250604 [FieldAssist] API - ContentProposalAdapter needs isShowing() method
Please implement a method ContentProposalAdapter.isShwoing(). The method should return a boolean whether the content assistant proposal popup is open or not.
bundles/org.eclipse.jface/src/org/eclipse/jface/fieldassist/ContentProposalAdapter.java
/*
		 * Select the proposal at the given index.
		 */
		private void selectProposal(int index) {
			Assert
					.isTrue(index >= 0,
							"Proposal index should never be negative"); 
			if (!isValid() || proposals == null || index >= proposals.length) {
				return;
			}
			proposalTable.setSelection(index);
			proposalTable.showSelection();
			showProposalDescription();
		}
		/**
		 * Opens this ContentProposalPopup. This method is extended in order to
		 * add the control listener when the popup is opened and to invoke the
		 * secondary popup if applicable.
		 * 
		 * @return the return code
		 * 
		 * @see org.eclipse.jface.window.Window#open()
		 */
		public int open() {
			int value = super.open();
			if (popupCloser == null) {
				popupCloser = new PopupCloserListener();
			}
			popupCloser.installListeners();
			IContentProposal p = getSelectedProposal();