[ONNX Editor] Use port indices instead of tensor names, new naming convention of inputs

[mbencer]

Ticket: 52743, 54016, 54933

• Introduced a new method of edge indication - by node index and input/output port index instead of node index and tensor name
• Changed way of creating new inputs: in general: cutting one edge causes the creation of new input (in general)
• Introduced a new naming convention for new inputs:
  -> the original name of an input tensor, if the tensor is consumed by only a one node
  -> first output name of an input tensor consumer + "/placeholder_port_" + port_index, if the tensor is consumed by more than one node (compatible with MO)
• Introduce a mechanism to provide custom input names

The review of this change was started in mbencer#3