Bug 164529 [FieldAssist] Provide the ability to listen to start and end field assist events
In the previous content assist functionality, an ICompletionListener could be specified to listen to the following events: public void assistSessionEnded(ContentAssistEvent event) public void assistSessionStarted(ContentAssistEvent event) The equivalent listener, IContentProposalListener, does not listen to those two events. PDE needs to know when an assist session is ended in order to reset the state it maintains for custom filtering of java type results. The current event does not handle the case where the user ends the content assist without selecting a proposal: public void proposalAccepted(IContentProposal proposal);
bundles/org.eclipse.jface/src/org/eclipse/jface/fieldassist/ContentProposalAdapter.java
* The keystroke that signifies content proposals should be shown.
	 */
	private KeyStroke triggerKeyStroke;
	/*
	 * The String containing characters that auto-activate the popup.
	 */
	private String autoActivateString;
	/*
	 * Integer that indicates how an accepted proposal should affect the
	 * control. One of PROPOSAL_IGNORE, PROPOSAL_INSERT, or PROPOSAL_REPLACE.
	 * Default value is PROPOSAL_INSERT.
	 */
	private int proposalAcceptanceStyle = PROPOSAL_INSERT;
	/*
	 * A boolean that indicates whether key events received while the proposal
	 * popup is open should also be propagated to the control. Default value is
	 * true.
	 */
	private boolean propagateKeys = true;
	/*
	 * Integer that indicates the filtering style. One of FILTER_CHARACTER,
	 * FILTER_CUMULATIVE, FILTER_NONE.
	 */
	private int filterStyle = FILTER_NONE;
	/*
	 * The listener we install on the control.
	 */
	private Listener controlListener;
	/*
	 * The list of listeners who wish to be notified when something significant