Better Darker Docs wot red

Provides custom scripts and styles to give the google docs suite a proper dark mode, including subpixel hinting (ClearType/TrueType) on text in docs and sheets.

Since this hooks document rendering, document appearance will be much more accurate than css-only modifications offered by other extensions.

Make sure to disable any other dark mode extensions for docs.google.com!

NOTE: By default, the dark theme will only be applied when website appearance is set to 'Dark' in Firefox settings, or when it is set to 'Auto' and Firefox is using a dark theme. Set dark mode to 'Always' to change this.