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.

IEC-61131 PLC programming
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Contents:

.. toctree::
   :maxdepth: 2

   create
   configuration
   edit
   connect
   run
   stdlib/index