Model Binder value API is not case-insensitive

[pimbrouwers]

Consider:

[<Fact>]
let ``StringCollectionReader value lookups are case-insensitive`` () =
    let values = 
        [ 
            "FString", [|"John Doe"; "Jane Doe"|] |> StringValues                
        ]
        |> Map.ofList
        |> fun m -> Dictionary(m)

    let scr = StringCollectionReader(values)

    // single values
    scr.TryGet "FSTRING"   |> Option.iter (should equal "John Doe")
    scr.TryGet "FString"   |> Option.iter (should equal "John Doe")
    scr.TryGet "fstriNG"   |> Option.iter (should equal "John Doe")
    scr?FSTRING.AsString() |> should equal "John Doe"
    scr?FString.AsString() |> should equal "John Doe"
    scr?fstrINg.AsString() |> should equal "John Doe"

    // arrays
    scr.TryArrayString "FSTRING" |> Option.iter (should equal [|"John Doe";"Jane Doe"|])
    scr.TryArrayString "fString" |> Option.iter (should equal [|"John Doe";"Jane Doe"|])
    scr.TryArrayString "fstriNG" |> Option.iter (should equal [|"John Doe";"Jane Doe"|])
    scr?FSTRING.AsArrayString()  |> should equal [|"John Doe";"Jane Doe"|]
    scr?fString.AsArrayString()  |> should equal [|"John Doe";"Jane Doe"|]
    scr?fstriNG.AsArrayString()  |> should equal [|"John Doe";"Jane Doe"|]