PLCgen: generate code/type dependencies file

For some target, like S7, the order in which for the generated code files the program blocks are created, matters for correct compilation. For instance, the user-defined types (UDTs) for tuple structs need to be considered in the right order. This is now documented (see !1066 (merged)). But, users then have to figure out the order themselves. It would be good if we could provide them with the order, like the example of #863 (comment 2824052). We should generate an extra file, with this information. Or, put it in the PLC code itself (for instance the MAIN file).

Addresses #679