TinyMCE: enable direct calls to `_WP_Editors::wp_mce_translation()`. When using TinyMCE directly, this makes it easier to load the translation of the default strings. Fixes #30293.

git-svn-id: https://develop.svn.wordpress.org/trunk@30296 602fd350-edb4-49c9-b593-d223f7449a82