Fonts Library: Fix variants count color contrast and l10n best practices

[afercia]

Description

The font variants count in the side panel has a very low color contrast ratio of 2.68:1

Also, concatenation with variables and translatable strings is not OK and doesn't meet the WordPress l10n best practices, even ore in this case where _n() is in use.

gutenberg/packages/edit-site/src/components/global-styles/font-family-item.js

Lines 35 to 38 in c6ac9c0

	<FlexItem style={ { color: '#9e9e9e' } }>
	{ variantsCount }{ ' ' }
	{ _n( 'variant', 'variants', variantsCount ) }
	</FlexItem>

Wirth also mentioning that, as far as I can tell, the gray #9e9e9e is not part of the established color palette. Such usage of unique, ad-hoc, colors shouldn't be allowed and, in any case, a sufficient color contrast ratio is a basic accessibility requirement. Also, inline styles should be avoided.

Introduced in #53884

Step-by-step reproduction instructions

• Go to Site editor > Styles > Typography
• Observe the text that indicates the font variants count has a very low color contrast ratio.

Screenshots, screen recording, code snippet

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Environment info

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Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes