Pass locale to wordpress.org theme/plugin API.

In the future this will be used to return localized plugin/theme info.

see #30735.
Built from https://develop.svn.wordpress.org/trunk@30944


git-svn-id: http://core.svn.wordpress.org/trunk@30933 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fifteen: hide search input cancel button. See #30728.
Built from https://develop.svn.wordpress.org/trunk@30945


git-svn-id: http://core.svn.wordpress.org/trunk@30934 1a063a9b-81f0-0310-95a4-ce76da25c4cd
About: Fix the WordPress badge.

`css-clean` (minifies our CSS) has an issue when using multiple backgrounds and background position together. Instead of relying on browser support for multiple backgrounds to display the WP logo as SVG, use the `.svg` CSS class.

see #30735.
Built from https://develop.svn.wordpress.org/trunk@30946


git-svn-id: http://core.svn.wordpress.org/trunk@30935 1a063a9b-81f0-0310-95a4-ce76da25c4cd