📝 Provide a description of the improvement

Mutating github.com//issues/12907 to improvement instead of new feature:

Allow mentions to fediverse actors, as when one is trying to use mention plugin in an application that uses activitypub is not possible to use the commonly used @[email protected] .

As contextual information, something like /(?<=^|[^\/[:word:]])@(([a-z0-9_]+([a-z0-9_\.-]+[a-z0-9_]+)?)(?:@([[:word:]\.\-]+[[:word:]]+))?)/ is used in some implementations
Be able to use @[email protected]

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