Dashicons: Update to the latest dashicons files.

props empireoflight, melchoyce.
fixes #26362.
Built from https://develop.svn.wordpress.org/trunk@26755


git-svn-id: http://core.svn.wordpress.org/trunk@26643 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Proper CSS specificity for columns-based dashboard grids.

props kovshenin.
fixes #26354.

Built from https://develop.svn.wordpress.org/trunk@26756


git-svn-id: http://core.svn.wordpress.org/trunk@26644 1a063a9b-81f0-0310-95a4-ce76da25c4cd