Swift: Implement ContentApprox

Author: hvitved

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

@@ -686,3 +686,10 @@ predicate additionalLambdaFlowStep(Node nodeFrom, Node nodeTo, boolean preserves
  * by default as a heuristic.
  */
 predicate allowParameterReturnInSelf(ParameterNode p) { none() }
+
+/** An approximated `Content`. */
+class ContentApprox = Unit;
+
+/** Gets an approximated value for content `c`. */
+pragma[inline]
+ContentApprox getContentApprox(Content c) { any() }