Ruby: Add AdditionalJumpStep class

Author: hmac

ruby/ql/lib/codeql/ruby/dataflow/internal/DataFlowPrivate.qll

@@ -1157,6 +1157,8 @@ predicate jumpStep(Node pred, Node succ) {
   succ.asExpr().getExpr().(ConstantReadAccess).getValue() = pred.asExpr().getExpr()
   or
   FlowSummaryImpl::Private::Steps::summaryJumpStep(pred, succ)
+  or
+  any(AdditionalJumpStep s).step(pred, succ)
 }
 
 private ContentSet getKeywordContent(string name) {
@@ -1484,3 +1486,15 @@ ContentApprox getContentApprox(Content c) {
   or
   result = TNonElementContentApprox(c)
 }
+
+/**
+ * A unit class for adding additional jump steps.
+ *
+ * Extend this class to add additional jump steps.
+ */
+class AdditionalJumpStep extends Unit {
+  /**
+   * Holds if data can flow from `pred` to `succ` in a way that discards call contexts.
+   */
+  abstract predicate step(Node pred, Node succ);
+}