IJavaSearchConstants.IMPLEMENTORS defines
"The search result is a type that implements an interface *or extends a
class*"

Change-Id: Ib419835ad411ccd83c246392a90406be32314f73
Reviewed-on: https://git.eclipse.org/r/c/jdt/eclipse.jdt.core/+/186393
Tested-by: JDT Bot <jdt-bot@eclipse.org>
Reviewed-by: Gayan Perera <gayanper@gmail.com>