Add ConditionGuardNode.getOutcome

Author: owen-mc

go/ql/lib/semmle/go/controlflow/ControlFlowGraph.qll

@@ -313,6 +313,8 @@ module ControlFlow {
      */
     Expr getCondition() { result = cond }
 
+    boolean getOutcome() { result = outcome }
+
     override Root getRoot() { result.isRootOf(cond) }
 
     override string toString() { result = cond + " is " + outcome }