[css-color-adjust] Add color-scheme to properties affected by forced color mode

[AmeliaBR]

As mentioned in #3881 (comment)

If the forced color scheme can be clearly identified as matching a dark or light mode (or any future named color schemes), activating that forced color mode should have the effect of setting color-scheme: <that-scheme> only.

Many of the normal color scheme effects might be further overridden by the forced colors (e.g., scrollbar colors), but the color scheme would provide the correct starting point.

If the author uses forced-color-adjust: none, they would also be cancelling out forced color-scheme related changes (other than those related to the normal color scheme preference mechanism).

[css-meeting-bot]

The CSS Working Group just discussed [css-color-adjust] Add color-scheme to properties affected by forced color mode, and agreed to the following:

• RESOLVED: add color-scheme to list of properties effected by forced-colors mode. Forced to value calculated based on colors used

The full IRC log of that discussion

<dael> Topic: [css-color-adjust] Add color-scheme to properties affected by forced color mode
<dael> github: https://github.com//issues/3885
<AmeliaBR> https://drafts.csswg.org/css-color-adjust-1/#forced
<dael> AmeliaBR: Posted a year ago. Some of spec has changed since
<dael> AmeliaBR: Spec text ^
<dael> AmeliaBR: It does say that when forced-colors mode is active UA accesses forced color colors and deterine if it's light or dark or inbetween. Treate as auto-flipping prefers color schedule ot light/dark/no preference
<dael> AmeliaBR: One thing missing is when it comes to properties effected. We're not reverting the color scheme property. If a website is using color-scheme to ask for dark mode form elements right now in spec we're not changing that if we force light mode. Seems like an oversight
<Rossen_> q?
<dael> AmeliaBR: Requested is add color-scheme to list of properties effected by forced-colors mode. Forced to value calculated based on colors used
<dael> Rossen_: Sound great. Any feedback?
<dael> fremy: sgtm
<dael> Rossen_: Objections?
<dael> RESOLVED: add color-scheme to list of properties effected by forced-colors mode. Forced to value calculated based on colors used
<dael> AmeliaBR: fantasai are you okay to do edits?
<dael> fantasai: Yep