Ruby: add SetterCallNode

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

@@ -150,6 +150,29 @@ class CallNode extends LocalSourceNode, ExprNode {
   }
 }
 
+/**
+ * A call to a setter method.
+ *
+ * For example,
+ * ```rb
+ * self.foo = 10
+ * a[0] = 10
+ * ```
+ */
+class SetterCallNode extends CallNode {
+  SetterCallNode() { asExpr().getExpr() instanceof SetterMethodCall }
+
+  /**
+   * Gets the name of the method being called without the trailing `=`. For example, in the following
+   * two statements the target name is `value`:
+   * ```rb
+   * foo.value=(1)
+   * foo.value = 1
+   * ```
+   */
+  final string getTargetName() { result = asExpr().getExpr().(SetterMethodCall).getTargetName() }
+}
+
 /**
  * An expression, viewed as a node in a data flow graph.
  *