C#: Consider Enums and System.DateTimeOffset as having a sanitizing effect.

csharp/ql/lib/semmle/code/csharp/frameworks/System.qll

@@ -756,6 +756,11 @@ class SystemDateTimeStruct extends SystemStruct {
   SystemDateTimeStruct() { this.hasName("DateTime") }
 }
 
+/** The `System.DateTimeOffset` struct. */
+class SystemDateTimeOffsetStruct extends SystemStruct {
+  SystemDateTimeOffsetStruct() { this.hasName("DateTimeOffset") }
+}
+
 /** The `System.Span<T>` struct. */
 class SystemSpanStruct extends SystemUnboundGenericStruct {
   SystemSpanStruct() {

csharp/ql/lib/semmle/code/csharp/security/Sanitizers.qll

@@ -57,8 +57,9 @@ class SimpleTypeSanitizedExpr extends DataFlow::ExprNode {
   SimpleTypeSanitizedExpr() {
     exists(Type t | t = this.getType() or t = this.getType().(NullableType).getUnderlyingType() |
       t instanceof SimpleType or
-      t instanceof SystemDateTimeStruct
-      // or t instanceof Enum
+      t instanceof SystemDateTimeStruct or
+      t instanceof SystemDateTimeOffsetStruct or
+      t instanceof Enum
     )
   }
 }