Add "Compare with/Replace with" actions to ResourceMappings

Add "Compare with/Replace with" actions to ResourceMappings

Add the eGit "Compare with/Replace with" actions to selections which
only adapt to ResourceMapping but not to IResource. This includes
objects like Java-WorkingSets and custom ResourceMappings.

ResourceMappings can be seen as a collection of resources forming a
logical model. It often makes sense to extend the navigator view to add
symbolic virtual nodes grouping the resources together. However since
there is no "real" resource, the virtual node adapts only to
ResourceMapping.

Selecting these ResourceMappings can be seen as selecting all resources
this mapping traverses. Since eGit's SelectionUtils already supports
ResourceMappings (collecting contained resources), selections adapting
only to ResourceMapping can be supported by simply enabling the actions
on them.

Bug: 474725
Signed-off-by: Stefan Dirix <sdirix@eclipsesource.com>
Change-Id: I6f967f72feae10cae29505fa17b81e65e0aa87de
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>