In advanced search, instead of empty scopes, show recently updated and created items

Problem to solve

Currently, when you load the advanced search page we show the counts of search results in a given scope. However, if you click on one of the scopes nothing happens but a page refresh; the scope you click isn't even selected. Additionally, we don't show anything to get the user started, but we could show results for each scope, for example sorted by updated date, similar to what the filtered views do.

Proposal

We should load a wildcard search for a selected scope in the background (i.e., don't populate the search bar with a *) and show the scope as selected, so that we don't confuse users with the current behavior described above. We should show the most recent items for a given scope based on:

• Issues: updated date desc.
• MRs: updated date desc.
• Projects: updated date desc.
• Code: updated desc. if we have it for files?
• Epics: updated date desc.
• Comments: created date desc.
• Users: created date desc.