3.0 - Terminal visual updates

[d0c-s4vage]

Describe the Feature Request
Embedded terminals aren't very customizable, and are hard to work with. Specifically:

• The surrounding box should be able to be styled, in the same way that quotes and tables can be styled/framed (specifically in 3.0)
• The surrounding box should also have a visual indicator on it that says:
  • if the terminal has focus
  • a reminder of the current keybinding to make it let go of focus

Example Markdown

Unfocused

   ┌───────────────────────────────┐
   │$>                             │
   │                               │
   │                               │
   │                               │
   └───────────────────────────────┘

Focused

   ┎───────────────────────────────┐
   ┃$>                             │
   ┃                               │
   ┃                               │
   ┃                               │
   ┖──────────────────────(ctrl+a)─┘

The terminal should also have a "focused" version of the surrounding box, with its own styles. The keybinding to escape would then be overlayed on top of that box in the bottom-right corner