add Inputs.file

[Fil]

closes #143

to test:

# Inputs.file

```js
const f = view(Inputs.file())
```

```js
f.sqlite()
```

```js
f.image()
```

[Fil]

A documentation/example could be a "data app" that allows the user to attach a file to a page and do some data processing (on an image, or an an excel file?)

[mbostock]

This will fix the built-in Inputs, but it doesn’t fix it when you import Inputs explicitly (which you have to do from an ES module) like so:

import * as Inputs from "npm:@observablehq/inputs";

So, we’ll either need to fix the resolution of npm:@observablehq/inputs to get a wrapper library with the fix, or we’ll need to publish a fix to Observable Inputs itself. I was expecting to do the latter given that we also need to fix the stylesheet #29.

[Fil]

Thanks, now I see the problem with this approach.

[Fil]

superseded by #469