Add ExtendedCall to PLCObject as a replacement of RemoteExec and reflect it in eRPC interface.

ExtendedCall is a generic remote procedure call that runtime code can register to and that IDE extensions can call.
For example a fieldbus extension can use ExtendedCall to browse the fieldbus devices connected to the runtime.

<?xml version='1.0' encoding='utf-8'?>
<OPCUAClient xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <AuthType/>
</OPCUAClient>