Improved UI for group forum threading settings
In #13341, there was some user confusion about the display of threaded content in a group forum. Whether it's displayed in a threaded way or in a linear way is controlled by a per-user setting, but this is not surfaced very well when looking at an individual thread, and it also means that logged-out users always see the default view (currently set to linear).
Let's consider the following:
1. Should we introduce a per-topic toggle? Something like: "Threaded view: On | Off" or "View replies as: Threaded | Unthreaded" or whatever. Where would this toggle appear on the page? Presumably it would be visible to all users (logged-in or otherwise) but would default to the global setting of the user. When implemented, we should be sure that the setting persists through pagination, so that if you click 'Threaded' and then go to page 2, it should be page 2 of threaded results (presumably via URL param)
2. What should be the default display? Currently, it's linear. I would suggest that perhaps it should be threaded. For discussions that have no inline replies, the threaded view is the same as the linear view. But for those that do have inline replies, it can be confusing to default to linear.
Tentatively placing in the 1.18.0 milestone.