If a meta box is registered with the `__block_editor_compatible_meta_box` set to `false`, it's indicating that it doesn't work in the block editor. If that's the case, we can add a place holder to inform the user that they'll need to use the classic interface to work with this meta box.
Props pento, jorgefilipecosta, peterwilsoncc, karmatosed, noisysocks, dd32, ocean90.
Merges [43941] and [43945] to trunk.
Fixes#45217.
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