C#: Add upgrade and downgrade scripts.

csharp/downgrades/fd04e45710e1988076801608abffdfa013b680fc/params.ql

@@ -0,0 +1,19 @@
+class Parameter extends @parameter {
+  string toString() { none() }
+}
+
+class TypeOrRef extends @type_or_ref {
+  string toString() { none() }
+}
+
+class Parameterizable extends @parameterizable {
+  string toString() { none() }
+}
+
+from
+  Parameter p, string name, TypeOrRef typeId, int index, int mode, Parameterizable parentId,
+  Parameter unboundId, int updatedMode
+where
+  params(p, name, typeId, index, mode, parentId, unboundId) and
+  if mode = 6 then updatedMode = 0 else updatedMode = mode
+select p, name, typeId, index, updatedMode, parentId, unboundId

csharp/downgrades/fd04e45710e1988076801608abffdfa013b680fc/upgrade.properties

@@ -0,0 +1,3 @@
+description: Extract `ref readonly` parameters as having `mode` 0 in the params table.
+compatibility: full
+params.rel: run params.qlo

csharp/ql/lib/upgrades/21ede72308c41493f19b37720d8259d5eb307f12/upgrade.properties

@@ -0,0 +1,2 @@
+description: Extract `ref readonly` parameters as having `mode` 6 in the params table.
+compatibility: backwards