Minor edits and clarifications in the color-gamut page

[dipikabh]

Description

FF110 now supports color-gamut.
The feature documentation already exists: https://developer.mozilla.org/en-US/docs/Web/CSS/@media/color-gamut

Some key edits done in this pull request:

• Instead of repeating the link to the glossary term 'gamut' in all descriptions, the link has been moved to the intro description
• The spec mentions both 'UA' and the output device support in each of the keyword values: https://drafts.csswg.org/mediaqueries-4/#color-gamut. Added that bit to the descriptions of the values.

Related issues and pull requests

Doc issue tracker: #23681

[github-actions]

Preview URLs

• /en-US/docs/Web/CSS/@media/color-gamut

External URLs (3)

URL: /en-US/docs/Web/CSS/@media/color-gamut
Title: color-gamut

• https://en.wikipedia.org/wiki/Rec._2020 (1 time) (Note! This may be a new URL 👀)
• https://en.wikipedia.org/wiki/SRGB (1 time) (Note! This may be a new URL 👀)
• https://www.color.org/chardata/rgb/DisplayP3.xalter (1 time) (Note! This may be a new URL 👀)