docs: interactive theme generator

[mariohamann]

For creating accessible themes that map to Solid's color an interactive and automatic theme generator was needed.

It serves the following purposes:

1. Automatically matches the luminescence of the Solid color scheme.
2. Offers the option to switch to a normalized luminescence, which might fit better especially in some tones like e. g. green tones, but could lead to decreasing accessibility.
3. Automatically generates CSS variables which can be copied to be used in themes.
4. Makes it possible to enable and disable the theme.

I've created some docs, too: https://64469bd84c5ea1ce2dd5d016-ztwobyajkn.chromatic.com/?path=/docs/docs-general-tokens--docs

CleanShot.2023-10-30.at.17.08.28.mp4

PR notes:

1. This is meant to be used by developer's, who might do this task several times, so I'm totally fine if not everyone finds it directly. UX of course could be improved, but after several trail and errors this was the best solution I could came up with where to place the tool.
2. As this is just some additional tooling, I decided to explicitly not use Solid Components (especially as they would have to be implemented differently, and we have React here, etc.)
3. I had to implement the option to normalize the colors, as this could otherwise lead to VERY dark colors when e. g. using green as primary color.