Stepper steps should display as a collapsible tree in sidebar table of contents

[matthew-voltera]

I love the stepper block for writing guides and instructionals. It would be helpful if the step titles displayed as a collapsible tree in the sidebar table of contents. This would help clean up the sidebar and clearly show which main process each step is under (in the case of multiple stepper blocks). Additionally, having the step number included in the sidebar would be helpful for user context and pathing as well.