Anchor tag helper should allow for multiple route value parameters with the same name

The [route values property](https://github.com/dotnet/aspnetcore/blob/2684644cea1322ebd213311293d93faf8d7e9bab/src/Mvc/Mvc.TagHelpers/src/AnchorTagHelper.cs#L137) in the anthor tag helper only allows for route values to have a single value since it of type `IDictionary`. Therefore when you say:

```
Link 1
```

If the query string is `?filter=Red&filter=Green` it produces:

```
Link 1
```

However if you say:

```
kvp.Key, kvp => (object?)kvp.Value))">Link 1
```

It correctly produces:

```
Link 1
```