Partially addresses #399.

Adds a typedValue[T] extension on HtmlInputElement[F] that returns the correct type based on the input type string:

• typedValue["file"] → F[FileList]
• typedValue["checkbox" | "radio"] → F[Boolean]
• typedValue["number" | "range"] → F[Double]
• anything else → F[String]

input.withSelf { self =>
  (
    typ := "file",
    onChange --> { _.evalMap(_ => self.typedValue["file"]).foreach(handleFiles) }
  )
}