Add support for background-less IconButtons

[rock3r]

Such icon buttons can be used when the icons are stateful and don't require a background being drawn — for example, for the clear button in a text field.

This should be fairly easy to do — providing no-background IconButtonColors variants in standalone and the bridge should be enough. We can also consider an entirely distinct IconButtonStyle and component, that wraps a regular one but replacing the style with the bg-less one.