TinyMCE: add stubs for the missing tinymce.util.Cookie, windowManager.onOpen...

TinyMCE: add stubs for the missing tinymce.util.Cookie, windowManager.onOpen and windowManager.onClose to the compat3x plugin. See #24067, fixes #26750.
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git-svn-id: https://core.svn.wordpress.org/trunk@26773 1a063a9b-81f0-0310-95a4-ce76da25c4cd