This new API will be called before the CompletionEngine creates
certain completion proposals like constructor and type proposals.

It allows to ignore the specified types in advance and improve
code completion performance.

Signed-off-by: Jinbo Wang <jinbwan@microsoft.com>
Change-Id: Iba6dc57efb0fffc1541469194bc95cef9cd29b5a
Reviewed-on: https://git.eclipse.org/r/c/jdt/eclipse.jdt.ui/+/191714
Tested-by: JDT Bot <jdt-bot@eclipse.org>
Reviewed-by: Roland Grunberg <rgrunber@redhat.com>