Administration: Attempt to even-out the new Up/Down arrows in metabox headings...

Administration: Attempt to even-out the new Up/Down arrows in metabox headings and make them look a bit better. Also group them a little closer together in an attempt to reduce confusion of having two down arrows next to one another. Move the focus outline to the button instead of only the icon.

Fixes #39074.
Built from https://develop.svn.wordpress.org/trunk@48465


git-svn-id: https://core.svn.wordpress.org/trunk@48234 1a063a9b-81f0-0310-95a4-ce76da25c4cd