Storybook: Fixed / Sticky top toolbar

[Lewiscowles1986]

Is your feature request related to a problem? Please describe.

I was frustrated when I began to use the Storybook components for a plugin, and noticed some holes. One of these is that if I add too many blocks to the playground, the Toolbar floats uncomfortably and gets further away, the further I scroll past what seems to be an equator (middle of my HD screen).

Describe the solution you'd like

Ideally, the functionality of the toolbar would allow it to be sticky, opaque, with high-enough ordering and so-on.

For now, I have a fix, which I would be happy to contribute to provide a Sticky BlockToolbar with controls fixed via hasFixedToolbar. I would like to know if you are open to PR on this.

Describe alternatives you've considered

I had considered not using Storybook.

I also considered looking for options, and there may be some, but I could not find them.

This may relate to #18619, which I see has been active since 2019.