Merge directories which contain a single subdirectory

In 2.8, code was added to automatically navigate to the next level when browsing returns a directory which contains a single subdirectory. This eliminates some clicks, but it doesn't have the best user experience. Navigation is still one step at a time, with each step paying the full roundtrip cost of talking to the server. It also interferes with navigation (BSERV-4090, BSERV-4783).

Instead of having the client automatically navigate, it would be better if, like Bitbucket Cloud, such directories were collapsed into a single step on the server.