Java: Don't clear content in store steps in summaries.

Author: aschackmull

java/ql/lib/semmle/code/java/dataflow/internal/DataFlowPrivate.qll

@@ -150,8 +150,7 @@ predicate readStep(Node node1, Content f, Node node2) {
  * in `x.f = newValue`.
  */
 predicate clearsContent(Node n, Content c) {
-  c instanceof FieldContent and
-  n = any(PostUpdateNode pun | storeStep(_, c, pun)).getPreUpdateNode()
+  exists(FieldAccess fa | instanceFieldAssign(_, fa) and n = getFieldQualifier(fa))
   or
   FlowSummaryImpl::Private::Steps::summaryClearsContent(n, c)
 }

java/ql/test/library-tests/dataflow/callback-dispatch/A.java

@@ -174,7 +174,7 @@ void foo3() {
     a1.field1 = source(20);
     A a2 = new A();
     applyConsumer1Field1Field2(a1, a2, p -> {
-      sink(p); // MISSING FLOW
+      sink(p); // $ flow=20
     });
     wrapSinkToAvoidFieldSsa(a1);
     sink(a2.field2);