Add ability to set arg index of virtualedges

Author: MarcMil

src/main/java/soot/jimple/toolkits/callgraph/VirtualEdgesSummaries.java

@@ -558,6 +558,10 @@ public boolean isBase() {
     public int getArgIndex() {
       return argIndex;
     }
+    
+    public void setArgIndex(int value) {
+      this.argIndex = value;
+    }
 
     public abstract VirtualEdgeTarget clone();