Editor: Improve the appearance of tag cloud in Tags meta box in classic editor.

Props sathyapulse, Spaceshipone, tmatsuur, audrasjb, afercia.
Fixes #48592.
Built from https://develop.svn.wordpress.org/trunk@46758


git-svn-id: https://core.svn.wordpress.org/trunk@46558 1a063a9b-81f0-0310-95a4-ce76da25c4cd