Accessibility: Customize: Improve focus styles for color picker and media...

Accessibility: Customize: Improve focus styles for color picker and media upload button in Customizer.

Props audrasjb, timhavinga, afercia, karmatosed.
Fixes #48694.
Built from https://develop.svn.wordpress.org/trunk@47208


git-svn-id: https://core.svn.wordpress.org/trunk@47008 1a063a9b-81f0-0310-95a4-ce76da25c4cd