A widget that makes underlying Text.rich or RichText animate like a typewriter.
Motivation
I was creating a visual novel engine,
so I needed a convenient way to animate RichTexts (with styles and WidgetSpans).
Actually there are some packages which do the thing, but they do not work with existent
RichTexts and/or do not support WidgetSpans.
In addition, it's also a kind of proof of concept in terms of interaction with the element tree.
Features
Wrap a Text.rich or a RichText to animate.
Supports trees of InlineSpan with arbitrary depth.
Can print both text characters and widgets.
Allows to set up different delays for different symbols.
Allows to call a function when the animation ends.