#14074 CellFilters: Hide empty case Data Filters node, add Filters submenu

The case-level Data Filters node (RimDataFilterCollection) was always shown under
RimEclipseCase, cluttering the tree when empty. Gate it in
RimEclipseCase::defineUiTreeOrdering on a new shouldBeVisibleInTree() check, and
refresh the owner case from onItemsChanged/onChildDeleted so the node appears and
disappears as the collection crosses the empty boundary.

Because a hidden node cannot be right-clicked to create the first filter, add a
RimEclipseCase::appendMenuItems override that exposes the filter-creation
commands as a Filters submenu on the case node. A shared
RicCellFilterFeatureTools::selectedDataFilterCollection() resolves a selected
RimEclipseCase to its data filter collection, so the cell, property and combined
filter create features target the case-level collection.

ApplicationLibCode/ProjectDataModel/RimEclipseCase.h

@@ -59,6 +59,11 @@ class RimEclipseResultAddressCollection;
 class RimEclipseViewCollection;
 class RimResultNameAlias;
 
+namespace caf
+{
+class CmdFeatureMenuBuilder;
+}
+
 //==================================================================================================
 //
 // Interface for reservoirs.
@@ -151,6 +156,7 @@ protected:
     void fieldChangedByUi( const caf::PdmFieldHandle* changedField, const QVariant& oldValue, const QVariant& newValue ) override;
     void childFieldChangedByUi( const caf::PdmFieldHandle* changedChildField ) override;
     void defineUiTreeOrdering( caf::PdmUiTreeOrdering& uiTreeOrdering, QString uiConfigName = "" ) override;
+    void appendMenuItems( caf::CmdFeatureMenuBuilder& menuBuilder ) const override;
 
     void resultAliasUiOrdering( caf::PdmUiOrdering& uiOrdering );