Docs - begin restructuring docs

Attempt to try and make the Lua docs digestible.

Main things changed:

• Some minor RST file structure changes
• Adds context badges instead of using text. These are also added to Lua annotation files with @context
• Move to a theme which supports dark/light mode automatically and is well maintained
• Remove some name noise, we don't need to prefix things with "built-in" and "OpenMW" everywhere. It's redundant.

Packages added:

• sphinx-design: Provides useful UI components like badges and tabbed content (see below)
• sphinx-copybutton: Adds a copy button to all code blocks (minus the luadocs generated ones, to be fixed later)
• Furo theme: Not the most beautiful, but more widely used and supported to reduce burden of maintaining a custom theme.

Things that need to be fixed:

- There are some minor styling issues with dark mode with Lua docs, these will require css overrides.