ATR-21896 : Add back vertex building even when no conversions

For some reason Legacy Trigger can attempt vertex building even with conversions disabled.

So lets leave / put back the doVertexBuilding flag to control this , independently of doConversion.

i.e reintroduce splitting of doVertexBuilding doConversion flags.

I honestly do not have traced the coupling of these 100% but seems to be there, and is not obvious yet to me where it comes from ...

Reconstruction/egamma/egammaRec/python/egammaRecFlags.py

@@ -59,8 +59,16 @@ class doBremFinding (egammaRecFlagsJobProperty):
     allowedTypes = ['bool']
     StoredValue = True
 
-# Other options
 
+class doVertexBuilding (egammaRecFlagsJobProperty):
+    """ switch for whether to do the conversion vertex building
+    """
+    statusOn = True
+    allowedTypes = ['bool']
+    StoredValue = True
+
+
+# Other options
 
 class doEgammaTruthAssociation (JobProperty):
     """ switch for truth association alg
@@ -144,7 +152,7 @@ jobproperties.add_Container(egammaRecFlags)
 
 # I want always the following flags in the container
 _list_Egamma = [Enabled, doEgammaCaloSeeded, doEgammaForwardSeeded,
-                doBremFinding, doConversions,
+                doBremFinding, doVertexBuilding, doConversions,
                 cellContainerName, doEgammaTruthAssociation,
                 clusterCorrectionVersion, calibMVAVersion, doSuperclusters,
                 inputTopoClusterCollection, egammaTopoClusterCollection]