Controlling memory location of od data

[cfr-mir]

Generate placeholders for storage attributes on OD data structures. make the "ROM" option matter.

[CANopenNode]

libedssharp has been forked to https://github.com/CANopenNode/CANopenEditor, I'm updating there. (In agreement with Robin Cornelius, updates will continue there, he is there also a maintainer.)

So I added this PR in https://github.com/CANopenNode/CANopenEditor, branch main. I also renamed attribute and added default definition, like so:

#ifndef OD_ATTR_PERSIST_COMM
#define OD_ATTR_PERSIST_COMM
#endif
extern OD_ATTR_PERSIST_COMM OD_PERSIST_COMM_t OD_PERSIST_COMM;
...

[CANopenNode]

This PR is not relevant any more, because it is included in https://github.com/CANopenNode/CANopenEditor.