[rustdoc search] sort stable items above unstable ones

[lolbinarycat]

I looked up "channel", clicked on the first result, copied that path to my code...

and was very surprised when i was actually using the unstable mpmc one instead of the stable mpsc channel.

I think name/path matching should generally take priority (otherwise people who are actually looking for unstable items would be massively inconvenienced), but when two items have the same distance, we should prioritize the one that is stable.

[lolbinarycat]

if this isn't already possible with the data in the search index, i believe the final tiebreak is the order in which things appear in the search index, so perhaps we could pre-sort that so all the stable options appear first?

[xizheyin]

I think this should allow the developer to make a choice. Maybe they can set different priorities for the pass attributes of these items.

[lolbinarycat]

@xizheyin this is a very niche situation, it requires two items that have the same name (or at least the same length of name and a common substring), it requires exactly one of them to be unstable (and thus it can only happen for stdlib types), and it requires a developer to search for that function, and only then will it result in a very small difference in sorting. adding an option here would be highly excessive.

[xizheyin]

Makes sense. I think we can indeed rank STABLE first