Paths should be / based on all platforms

[haraldsteinlechner]

Currently platform specific paths can leak between platforms via scene files. Dealing with this robustly is source of confusion for quite some time and is getting more complex with .net 8 giving up on backslash mapping.
Sequenced bookmark paths are IMO not fixable in retrospective, thus for those i suggest a transition phase:

• create only / based paths
• if \\ path is found, try to fix it when resolving the file (on usage side).