Ruby: add query for measuring call graph

ruby/ql/src/queries/meta/CallGraph.ql

@@ -0,0 +1,15 @@
+/**
+ * @name Call graph
+ * @description An edge in the call graph.
+ * @kind problem
+ * @problem.severity recommendation
+ * @id rb/meta/call-graph
+ * @tags meta
+ * @precision very-low
+ */
+
+import codeql.ruby.AST
+
+from Call invoke, Callable f
+where invoke.getATarget() = f
+select invoke, "Call to $@", f, f.toString()