Fuzzy finder: default ordering should list recently opened files at the top

Created by: olafurpg

Currently, the default ordering of the fuzzy finder when there is no query is to list all the files in the original order (not sorted). It would be nice if the default order displayed recently opened files at the top.

Originally suggested by @tsenart in https://github.com/sourcegraph/sourcegraph/issues/21201#issuecomment-863051357

Olaf: can you give a concrete example that compares the current ordering with frecency ordering? Tomas: I'm talking about the original ordering, before the user inputs anything at all. It's a nice way to quickly jump to recent files when you don't necessarily remember the name. It's definitely a nice to have, not a must.