Introduces `WP_Customize_Partial::check_capabilities()` for parity with `WP_Customize_Control::check_capabilities()`. See #27355. Fixes #35914. Built from https://develop.svn.wordpress.org/trunk@36643 git-svn-id: http://core.svn.wordpress.org/trunk@36610 1a063a9b-81f0-0310-95a4-ce76da25c4cd