HTML API: Escape script tag contents automatically.

When setting JavaScript or JSON script tag content, automatically escape sequences like `<script>` and `</script>`. This renders the content safe for HTML. The semantics of any JSON and virtually any JavaScript are preserved.

Script type detection follows the HTML standard for identifying JavaScript and JSON script tags. Other script types continue to reject potentially dangerous content.

Developed in WordPress/wordpress-develop#10635.

Props jonsurrell, dmsnell, westonruter.
Fixes #64419. See #63851, #51159.


Built from https://develop.svn.wordpress.org/trunk@61477


git-svn-id: http://core.svn.wordpress.org/trunk@60789 1a063a9b-81f0-0310-95a4-ce76da25c4cd

Author: sirreal