Autocomplete suggestions: do not wait for fechSuggestions() to emit before showing static suggestions

Created by: lguychard

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

Steps to reproduce:

1. Type in "repo" in the search bar

Expected behavior:

Filter suggestions are immediately shown. Fuzzy suggestions are shown eventually, once they are fetched.

Actual behavior:

The suggestions dropdown is only shown when fuzzy suggestions have been fetched.

I think the suggestions dropdown would feel a lot more reactive if static suggestions were shown immediately (and then eventually merged with fuzzy suggestions).

This could be easily done with something like this:

merge(
    of(staticSuggestions),
    fetchSuggestions().pipe(
        map(backendSuggestions => [...staticSuggestions, ...backendSuggestions])
    )
)