[css-color-adjust-1] Expand on how forced colors mode handles emojis (#12892)

* update forced colors emoji wording

* add specifics on when the property is forced

* update to computed value time

Author: alisonmaher

css-color-adjust-1/Overview.bs

@@ -600,7 +600,8 @@ Properties Affected by Forced Colors Mode {#forced-colors-properties}
 	* 'scrollbar-color' computes to ''scrollbar-color/auto''
 	* 'accent-color' computes to ''accent-color/auto''
 	* If 'font-variant-emoji' computes to ''font-variant-emoji/normal'' or ''font-variant-emoji/unicode'',
-		UAs should force any emoji on the page to its monochrome variant, if available.
+		UAs should force any emoji on the page to its monochrome variant, if available,
+		by forcing the [=computed value=] of 'font-variant-emoji' to ''font-variant-emoji/text''.
 
 	UAs may further tweak these <a>forced colors mode</a> heuristics
 	to provide better user experience.