Add `showModal` and `close` functions for `HTMLDialogElement`

[jquesada2016]

Prerequisites

• [ x ] Before opening an issue, please check the HTML standard (https://html.spec.whatwg.org). If it doesn't appear in this spec, it may be present in the spec for one of the other purescript-web projects. Although MDN is a great resource, it is not a suitable reference for this project.

Description

showModal and close functions should be added for HTMLDialogElement.