feature request: SceneToolbarButton should support text and tooltips

[joeblubaugh]

SceneToolbarButton has a state object:

interface ToolbarButtonState extends SceneObjectState {
    icon: IconName;
    onClick: () => void;
}

but this doesn't support a text value, which is a pretty important usability and accessibility feature. It also doesn't support a tooltip, so hovering also can't be used to understand the control's function.

The rendered HTML also doesn't include information that can be used to understand the button's purpose.