Multiple network signal sections

[Sharparam]

Description

It would be nice if, like for cargo signals, we can have section support for the network signals.

Context

This will let us create sections for shared/non-shared networks, which might be useful. It will also let us reduce the amount of special handling of sections particularly when copying or upgrading from other combinators.

Implementation

UI needs to be updated to be able to show multiple sections in the network signal area. We'd also have to re-think how to create and update network signals, as the current "button and textbox at the top" might not transfer well to having multiple sections.

One way could be to have a button in each section that will open the encoder UI to create a new network signal for that section (for updating this is already functional by ctrl-clicking on a signal).

This does mean you will be required to use the encoder UI for network signals, but if we ensure it's smooth enough to work well with keyboard support for confirmation, it might be a worthwhile trade-off? (Unless we can continue to have an input method directly in each section that works well.)