[PATCH] Add completion styling

[Eli Zaretskii]

> Cc: gdb-patches@sourceware.org
> From: Pedro Alves <palves@redhat.com>
> Date: Sun, 24 May 2020 13:58:02 +0100
> 
> Try "b main[TAB]" when debugging GDB, and you'll see that GDB
> highlights the "t" as the first different character here:
> 
> selftests::string_view::cons_1::main()
> selftests::string_view::cons_2::main()
> selftests::string_view::cons_3::main()
>     ^
> 
> while it should highlight here:
> 
> selftests::string_view::cons_1::main()
> selftests::string_view::cons_2::main()
> selftests::string_view::cons_3::main()
>                                     ^

Really? not here:

 selftests::string_view::cons_1::main()
                              ^

But I actually don't understand how did we get these candidates by
typing "main".  Don't we complete by looking for strings that begin
with what the user typed?  I'm probably missing something here.