[PopupMenu] Apply a shapeAppearance style to a PopupMenu

Nobody has claimed this yet.

I am using the latest version

com.google.android.material:material:1.1.0-alpha09

According to [documentation][2] it is possible to customize the component shapes using the **`shapeAppearanceOverlay`** attribute in the style.
These components should be supported:

- Bottom Sheet
- Button
- Floating Action Button
- Card
- Chip
- Dialog
- Menu
- Text Field

I am able to apply the attribute to these components except the [Menu][3], in particular `PopupMenu`. I was looking for it in the material themes but I didn't find it.
I tried something like that, but it doesn't work:

<item name="shapeAppearanceOverlay">@style/ShapeAppearanceOverlay.MyApp.PopupMenu</item>



<item name="cornerFamily">cut</item>
<item name="cornerSize">32dp</item>

[1]: https://github.com/material-components/material-components-android
[2]: https://github.com/material-components/material-components-android/blob/master/docs/theming/Shape.md#supported-components
[3]: https://github.com/material-components/material-components-android/blob/master/docs/components/Menu.md

Start with the linked Shape.md and Menu.md documentation, then trace how PopupMenu styles are defined and applied. Done means a PopupMenu can use the documented shapeAppearanceOverlay customization, with the relevant behavior covered by the project's tests.

Written by the indexing model from the issue text.