title: VSCode extension api – file type/extension icons using ThemeIcon
body: <p>We are building an extension that visualizes some data for workspace files in our view using a class derived from <code>TreeDataProvider</code>. We wonder if there is a way to use file icons contributed by the current File Icons Theme for our custom tree items. Base icon class has a field <code>icon: ThemeIcon</code> which supports product icons. Wonder if something similar exists for referring to file-type icons?</p>
  <p>Thanks</p>