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
if (adapter instanceof IControlContentAdapter2) {
				selectionRange = ((IControlContentAdapter2) adapter)
						.getSelection(control);
			}
		}
	}
	/*
	 * Get the proposals from the proposal provider. Gets all of the proposals
	 * without doing any filtering.
	 */
	private IContentProposal[] getProposals() {
		if (proposalProvider == null || !isValid()) {
			return null;
		}
		if (DEBUG) {
			System.out.println(">>> obtaining proposals from provider"); 
		}
		int position = insertionPos;
		if (position == -1) {
			position = getControlContentAdapter().getCursorPosition(
					getControl());
		}
		String contents = getControlContentAdapter().getControlContents(
				getControl());
		IContentProposal[] proposals = proposalProvider.getProposals(contents,
				position);
		return proposals;
	}
	/**
	 * Autoactivation has been triggered. Open the popup using any specified