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.

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<?xml version="1.0" encoding="UTF-8"?>

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<BaseParams Name="py_ext_0" IEC_Channel="0"/>