StoryTextChange
data class StoryTextChange(val storyStep: StoryStep, val position: Int) : BackstackAction, SingleAction
A change in the text of the story. There's a separation between StoryTextChange and StoryStateChange because StoryTextChange and not saved as a unit for usability and performance reasons. A user wouldn't like to revert character by character so the BackstackManager must handle merging them.