Add vertical scrolling to the Wiki editors

Problem to solve

When editing longer pages in the Wiki, the editor will grow in size to the point where the toolbar icons are no longer visible on the screen. When writing in Markdown, this is less of a problem because 1) there are fewer buttons in the toolbar and 2) most people can or prefer to write Markdown directly.

However, in the Content Editor, the toolbar is a more critical component of the editor. Having this UI unavailable on the screen becomes a hassle and requires distracting scrolling to access core features.

Proposal

Mimic the behavior of the issue description editor.

1. Start small. The size of the editor on a new page is great.
2. Grow as I type some content. It's helpful to scale the editing area as my content grows.
3. Have a maximum height. At a certain point, the field is too tall to fit in my browser window.
4. At the max height, introduce a vertical scroll to ensure the toolbar is available at all times

We should do this for the "classic" wiki editor and the Content Editor.

Questions

1. What is the correct max height? Is this something we can do based on relative line height or current window size? Or does it have to be hard-coded at some line length?
2. What do we lose here? Mid-page scrolling can be tricky on mobile but are there any other concerns? Will this impact our implementation of the floating bubble menu with formatting controls?