add callgraph test

ql/test/callgraph/Foo.qll

@@ -0,0 +1,15 @@
+import ql
+
+predicate foo() { none() }
+
+query predicate test() { foo() }
+
+class Foo extends AstNode {
+  predicate bar() { none() }
+
+  predicate baz() { bar() }
+}
+
+class Sub extends Foo {
+  override predicate baz() { super.baz() }
+}

ql/test/callgraph/callgraph.expected

@@ -0,0 +1,3 @@
+| Foo.qll:5:26:5:30 | PredicateCall | Foo.qll:3:1:3:26 | foo |
+| Foo.qll:10:21:10:25 | PredicateCall | Foo.qll:8:3:8:28 | ClassPredicate |
+| Foo.qll:14:30:14:40 | MemberCall | Foo.qll:10:3:10:27 | ClassPredicate |

ql/test/callgraph/callgraph.ql

@@ -0,0 +1,3 @@
+import ql
+
+query AstNode getTarget(Call call) { result = call.getTarget().getDeclaration() }