C#: Add upgrade and downgrade scripts.

Author: michaelnebel

csharp/downgrades/81a394bedda3d4747e36496c7be4d958424636d6/expressions.ql

@@ -0,0 +1,13 @@
+class Expression extends @expr {
+  string toString() { none() }
+}
+
+class TypeOrRef extends @type_or_ref {
+  string toString() { none() }
+}
+
+from Expression e, int k, int kind, TypeOrRef t
+where
+  expressions(e, k, t) and
+  if k = 135 then kind = 106 else kind = k
+select e, kind, t