PLCgen: ambiguities in IO test

This issue contains description and discussion about the following ambiguities detected in IO test:

• IO definition of LREAL;
• allocation of DInt on the analog IO (channel);
• allocation of LREAL on the analog IO (channel).

(test set: plcgen-test-models-v32; hardware target: S7-1200; test environment: TIA Portal V19)

Addresses: #1019 (closed), #679, #798 (closed)