Make sure the $parent argument of wp_insert_attachment() still works as expected after [28579].

Merges [29745] to the 4.0 branch.

props jesin, dikiy_forester.
fixes #29646.

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Avoid PHP notices in media modal caused by orphaned attachments.

Merges [29724] to the 4.0 branch.

props SergeyBiryukov.
fixes #29566.

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Create correct permalinks for child posts of hierarchical post types when default permalinks are used.

Merges [29765] to the 4.0 branch.

props loushou.
fixes #29615.

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In `wp_audio|video_shortcode()`, make sure that `autoplay` and `loop` are booleans. Passing `'false'` to them will force them to be active, which is bad. 

Merges [30185] to the 4.0 branch.

props wonderboymusic.
fixes #29825.

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