Add High/Low Contrast Themes for light sensitive users

[Sarenor]

Describe what feature you'd like. Pseudo-code, mockups, or screenshots of similar solutions are encouraged!

A Low-contrast, low-intensity theme. Potentially automatically selected when the low-contrast media query applies.

What type of pull request would this be?

Enhancement

Any links to similar examples or other references we should review?

No response

[endigo9740]

Per prior request in the PR, let's fold this into the same issue:
#1154

[endigo9740]

This issue has been consolidated into the linked theme generator updates ticket.