Widget Customizer: Set hightlight color to blue. Same color as in [27741].

fixes #27358.
Built from https://develop.svn.wordpress.org/trunk@27814


git-svn-id: http://core.svn.wordpress.org/trunk@27648 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Introduce `pre_update_option` filter.

Filter is available in update_option() and allows to filter any option before its value is (maybe) serialized and updated.

see #27504.
props westonruter.

Built from https://develop.svn.wordpress.org/trunk@27815


git-svn-id: http://core.svn.wordpress.org/trunk@27649 1a063a9b-81f0-0310-95a4-ce76da25c4cd