clarify behavior of opening a new tab

[skybrian]

While working on a program in dartpad, I wanted to create a second dartpad for an experiment. I duplicated the tab, and it showed the same program as before, with the same name at the top. So I thought it was another view of the same buffer.

This isn't the case; if you edit the second tab, it's actually independent of the first. This is what I wanted, but reusing the same name (steep-band-6287) makes it look like they're the same.

Perhaps this name should be changed when opening a new tab, if they're actually independent? It's unclear what this name is for.

[kwalrath]

This seems like a very reasonable usability request.

[skybrian]

Verified that the behavior is still as described.

[RedBrogdon]

Still an issue. Adding to backlog.

[parlough]

Closing in favor of #2871 as the current UI doesn't support saving/loading anymore. If anyone would like us to bring that, please upvote that issue. Thanks so much!