Update GetDeclarationListSymbols to expose FSharpSymbolUse

This allows the display context to be used during formatting so the current open statements are taken into consideration.

**Note:** I had to move `FSharpSymbolUse` further up `service.fs` so that `FSharpSymbolUse` could be referenced by `x.GetDeclarationListSymbols`
and the _m ?

> On 3 Dec 2014, at 19:56, Don Syme <notifications@github.com> wrote:
> 
> In src/fsharp/vs/service.fs:
> 
> > @@ -1006,7 +1027,10 @@ type TypeCheckInfo
> >                          items |> List.map (fun (_nm,itemsWithSameName) -> 
> >                              match itemsWithSameName with
> >                              | [] -> failwith "Unexpected empty bag"
> > -                            | items -> items |> List.map (fun item -> FSharpSymbol.Create(g, thisCcu, tcImports, item)))
> > +                            | items ->
> > +                                items 
> > +                                |> List.map (fun item -> let symbol = FSharpSymbol.Create(g, thisCcu, tcImports, item)
> > +                                                         FSharpSymbolUse(g, _denv, symbol, ItemOccurence.Use, _m)))
> Change _denv to denv now it's actually being used :)
> 
> —
> Reply to this email directly or view it on GitHub <https://github.com/fsharp/FSharp.Compiler.Service/pull/281/files#r21259808>.
>