Customize: Add additional filters to Customizer to prevent JSON corruption.

This solution extends the wp_insert_post_data filter to pass in addition to the slashed/sanitized/processed data, and the slashed/sanitized/unprocessed data, to also pass the initial slashed/unsanitized/unprocessed data which was passed into wp_insert_post(). This then allows plugins to have complete control over how sanitization is performed based on the post type.

Props westonruter, peterwilsoncc, sstoqnov, whyisjake, xknown.
 

Built from https://develop.svn.wordpress.org/trunk@47633


git-svn-id: https://core.svn.wordpress.org/trunk@47408 1a063a9b-81f0-0310-95a4-ce76da25c4cd