In `WP_Query::get_queried_object()`, account for `pre_get_posts` by checking for `tag` when `tag_id` isn't present. Tags still need to be rolled up into `tax_query`. Add a unit test confirming expected query vars during and after `pre_get_posts`.

Props mattonomics for a patch.
See #27362.


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Change string "Create Playlist" to "Create Audio Playlist." Open new tickets for individual issues.

Fixes #26631. 


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