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.

PLC variables and local variables
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PLC variables start with ``/``
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Local Page variables start with ``.``
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Local HMI variables
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