org.eclipse.ui.workbench

Converted Object getAdapter(Class) to <T> T getAdapter(Class<T>) in
org.eclipse.ui.internal.util.Util and org.eclipse.ui.part.WorkbenchPart
classes and cleaned up all the "unnecessary cast" warnings coming from
them and the already generified version of
Platform.getAdapterManager().getAdapter().

Change-Id: I49389a9e978be67b31a0394c98b7441acbad3057
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>