Support asp-items for datalist element

The [`` element](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/datalist) can be used to create a HTML-only "type-to-select" drop-down list (aka combobox with input enabled).

The elements with the `` tag are of type ``, just like those that would be in a `` list, which is supported by the `asp-items` Razor tag helper.

e.g. it would be great to be able to turn

```html

```

into

```html

```

But perhaps it would be necessary for the tags to be coalesced into one, so that one need not type out and match the `id` tag, in which case it might look something like this:

```html

```