C#: Do not clear content of collection type struct fields.

Author: michaelnebel

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

@@ -6,6 +6,7 @@ private import ControlFlowReachability
 private import FlowSummaryImpl as FlowSummaryImpl
 private import semmle.code.csharp.dataflow.FlowSummary as FlowSummary
 private import semmle.code.csharp.dataflow.internal.ExternalFlow
+private import semmle.code.csharp.commons.Collections
 private import semmle.code.csharp.Conversion
 private import semmle.code.csharp.dataflow.internal.SsaImpl as SsaImpl
 private import semmle.code.csharp.ExprOrStmtParent
@@ -2528,6 +2529,7 @@ private predicate clearsCont(Node n, Content c) {
     a.getType() = s and
     f = s.getAField() and
     c.(FieldContent).getField() = f.getUnboundDeclaration() and
+    not f.getType() instanceof CollectionType and
     not f.isRef()
   )
   or