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'?>
<MQTTClient xmlns:xsd="http://www.w3.org/2001/XMLSchema" Broker_URI="wss://192.168.19.25:18885">
  <AuthType>
    <x509 Client_certificate="" Broker_certificate="test-root-ca.crt" Verify_hostname="false"/>
  </AuthType>
</MQTTClient>