C#: Add some test cases for methods that are not properly exposed and will this not get their summary captured.

csharp/ql/test/utils/model-generator/CaptureSummaryModels.expected

@@ -1,3 +1,4 @@
+| NoSummaries;PublicClassFlow;false;PublicReturn;(System.Int32);Argument[0];ReturnValue;taint |
 | Summaries;BasicFlow;false;ReturnField;();Argument[Qualifier];ReturnValue;taint |
 | Summaries;BasicFlow;false;ReturnParam0;(System.String,System.Object);Argument[0];ReturnValue;taint |
 | Summaries;BasicFlow;false;ReturnParam1;(System.String,System.Object);Argument[1];ReturnValue;taint |

csharp/ql/test/utils/model-generator/NoSummaries.cs

@@ -0,0 +1,45 @@
+using System;
+
+namespace NoSummaries;
+
+// Single class with a method that produces a flow summary.
+// Just to prove that, if a method like this is correctly exposed, a flow summary will be captured.
+public class PublicClassFlow
+{
+    public int PublicReturn(int input)
+    {
+        return input;
+    }
+}
+
+public sealed class PublicClassNoFlow
+{
+    private int PrivateReturn(int input)
+    {
+        return input;
+    }
+
+    internal int InternalReturn(int input)
+    {
+        return input;
+    }
+
+    private class PrivateClassNoFlow
+    {
+        public int ReturnParam(int input)
+        {
+            return input;
+        }
+    }
+
+    private class PrivateClassNestedPublicClassNoFlow
+    {
+        public class NestedPublicClassFlow
+        {
+            public int ReturnParam(int input)
+            {
+                return input;
+            }
+        }
+    }
+}