Prevents slashes from being added when a user without `unfiltered_html` previews a nav menu item containing an apostrophe or some other slashable character, and prevents the loss of an intentional slash (e.g. "\o/") when saving a nav menu item, regardless of capability. Fixes #35869. Built from https://develop.svn.wordpress.org/trunk@36608 git-svn-id: http://core.svn.wordpress.org/trunk@36575 1a063a9b-81f0-0310-95a4-ce76da25c4cd