Proposal: Add a Feed type

[habrahamsson-skanetrafiken]

We are currently representing feed ids as String feedId and these strings are passed around and used to create FeedScopedIds. I propose to instead add a specific type Feed to use instead of using strings. This Feed will act as a factory for FeedScopedId. This would give us a bit of type safety and get better control of how FeedScopedIds are created.

See PR #6516 for an illustration of what this could look like.

Before:

void doSomething(String feedId, ...) {
  ...
  var id = new FeedScopedId(feedId, netexId);
  ...
}

After:

void doSomething(Feed feed, ...) {
  ...
  var id = feed.scopedId(netexId);
  ...
}

What do people think about this?

[miklcct]

I think it is a good idea, however, FeedScopeId also need to be changed to use this new type as the member as well.