Add Silk support for FileInputs

If you create an `Input(InputType.File)` right now, it looks really bad.

```kotlin
var filePath by remember { mutableStateOf("") }
Input(InputType.File, filePath, onValueChange = { filePath = it }, Modifier.id("file-input"))
```

We should figure out a way to make this look good, possibly by tweaking Input styles, and/or introducing a FileInput composable into Silk (not sure yet)