Autocomplete suggestions: comprehensive list of filters is never shown

Created by: lguychard

• Sourcegraph version: sourcegraph/server:3.10.0-rc.2

This might actually be expected now (and if so, close this). @christinaforney can you chime in on what we want here? I remember raising it in code review and being told that this was actually desirable (and growing to like it during that round of testing), so I'm filing in case it was removed unintentionally.

Steps to reproduce:

1. In the search query field, type in a valid filter with a value (for example repo:^some/repo$), then a space.

Expected behavior:

All valid filters are suggested:

Actual behavior:

Only "legacy" suggestions are shown: