add none option in Shape (Legacy)

[politerakib]

[romannurik]

What's the rationale for this? The last several versions of Android have forced a specific shape on icons.

[martin-braun]

@romannurik I need this as well to export the ic_launcher_foreground.png for a legacy app. There is no time to modernize this code right now.

Could you please bring it back?