Twenty Sixteen: Fix superscript and subscript.

When using the block-based editor in Twenty Sixteen, superscript is displaying below the baseline and subscript is displaying above the baseline. This is the opposite of what should occur. This reverses the two to display correctly.

Props greg-raven, torontodigits, JDTrower.

Merges [44210] into trunk.

Fixes: #44776.
Built from https://develop.svn.wordpress.org/trunk@44311


git-svn-id: https://core.svn.wordpress.org/trunk@44141 1a063a9b-81f0-0310-95a4-ce76da25c4cd