LF: ContractInstance should be a CidContainer

In #11419 we drop the implicit call that convert ContractInstance in
CidContainer. Thie is used by Canton and should be restore.

Note that now ContractInstance is not polymorphic anymore, hence we
can inherite CidContainer instead of defining an implicit.

CHANGELOG_BEGIN
CHANGELOG_END

daml-lf/transaction/src/main/scala/com/digitalasset/daml/lf/value/Value.scala

@@ -202,7 +202,9 @@ object Value {
       template: Identifier,
       arg: Value,
       agreementText: String,
-  ) {
+  ) extends CidContainer[ContractInstance] {
+
+    override protected def self: this.type = this
 
     def map(f: Value => Value): ContractInstance =
       copy(arg = f(arg))