Composition: large input modal

### As a `content author` I want `a larger composition area` so that `I can see more of my content as I'm writing`.

**Is your feature request related to a problem? Please describe.**
Writing takes a lot of focus, especially when there's a lot going on. How might we help content authors focus while content authoring when they need it?

**Describe the solution you'd like**
One idea is to offer a large `modal` they would be able to launch when they needed to see more of their content, and focus on authoring.

Abstract spec: https://share.goabstract.com/599392a5-920a-4ed3-9aeb-a843ba67eaab?mode=design

**Describe alternatives you've considered**
A clear and concise description of any alternative solutions or features you've considered.

**Additional context**
Add any other context or screenshots about the feature request here.