Autoprefixer for [39249].

Fixes one errant value and re-aligns some existing prefixed property values so they don't get doubled when precommit/postcss is run again in the future.

props davidakennedy.
see #29158.

Built from https://develop.svn.wordpress.org/trunk@39301


git-svn-id: https://core.svn.wordpress.org/trunk@39241 1a063a9b-81f0-0310-95a4-ce76da25c4cd