This aims to avoid slowing down the post editing by using a cached value instead of calling `get_users()`, which can be slow when plugins add various filters to all `get_users()` calls, especially with meta value comparisons on large `user_meta` tables.
Follow-up to [24304], [24543], [41829], [53011], [53018].
Props berislav.grgicak, bor0, costdev.
See #55958.
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