[27640] supported a caption for audio and video shortcodes as part of a UX iteration for the related MCE views. These captions have since be excluded, so the extra code should be removed (it was there for this sole reason).

See #27320.


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Only set the `poster` attribute automatically for videos when the image does not match the default mime-type icon. `wp_prepare_attachment_for_js()` is used in multiple contexts. This context requires disambiguation.

See [27659].


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Heartbeat: no longer "experimental", see #25272
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Add a note that wpView is "experimental", see #26959
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