Toolbar: Increase admin bar height to 48px for desktop and mobile

[dilipom13]

Summary

• Sets the admin Toolbar to a consistent 48px height on desktop and responsive views (Trac #65881).
• Updates --wp-admin--admin-bar--height and the front-end bump styles so content clears the taller Toolbar.
• Adjusts Twenty Twenty and Twenty Twenty-One offsets that previously assumed 32px / 46px.

Test plan

• While logged in, confirm the Toolbar is 48px in wp-admin and on the front end
• Confirm front-end content sits below the Toolbar with no overlap
• Below 782px width, confirm the Toolbar stays 48px and items remain easy to use
• Open the WP logo and My Account menus and confirm they align under the Toolbar
• With Twenty Twenty and Twenty Twenty-One, spot-check sticky/header positioning with the admin bar visible

Trac: https://core.trac.wordpress.org/ticket/65881

[github-actions]

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Props dilip2615.

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[github-actions]

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[dilipom13]

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