ParaView's selection-handling rewrites the VTK selection created
during pick events, dropping information that SMTK needs to recover
component IDs. To address this, ParaView has moved its rewrite
logic into a new class, named `vtkPVEncodeSelectionForServers`,
which applications (or plugins) can override using the vtkObjectFactory.

SMTK now overrides creation of this class, returning a custom subclass
named `vtkSMTKEncodeSelection`. This class is created on the client
and dispatches ParaView selections to operations in a new group
(VTKSelectionRespondersGroup). These operations are provided access
to the client-side SMTK selection instance and the first operation
to process a given resource is accepted as the selection updater
for that resource.

This commit also adds a toolbar filter-option for selecting instance
entities and an icon for instances in the resource browser widget.