Update TinyMCE for [25187]. see #25131.

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Improve clarity and speed of [25320] (merged as [25325]). Merges [25338] to 3.6.

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Avoid string offset notices in [25319] (merged as [25324]). Merges [25340] to 3.6.

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Avoid error in ms-files.php after [25317] (merged as [25322]). Merges [25344] to 3.6.

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