Adopt Package Explorer, Outline view contribution and editor breadcrumb
for Java editor to use new JFace API that allows viewers display huge
number of elements without freezing UI.

See https://github.com/eclipse-platform/eclipse.platform.ui/issues/818
and https://github.com/eclipse-platform/eclipse.platform.ui/pull/810.

Fixes https://github.com/eclipse-jdt/eclipse.jdt.ui/issues/631