When using WP_Query's `"fields" => "ids"` (or `"fields" => "id=>parent"`), the returned values should be an array of integers, not array of integers represented by strings.

Adds unit tests. All other unit tests pass.

Props danielbachhuber.
Fixes #27252.


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Media manager: Avoid a blank modal when an invalid image size class is set on the image.

props gcorne.
fixes #24409.

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Customizer header images: Fix randomizing headers.

props mcsf.
see #21785.

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When using `meta_query` in a `WP_Query`, passing `NOT EXISTS` or `''` to `compare` should not require `value` to be set. The resulting SQL should then produce the appropriate `OR` clause for existence of non-existence after passing the query to the `$key_only_queries` stack internally.

Adds unit tests. 

Props chrisguitarguy, for the original patch.
Fixes #23268.


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In `wp_create_post_autosave()`, intersect the `$new_autosave`'s keys with the keys from `_wp_post_revision_fields()` to ensure that all expected fields are present.

Props kovshenin.
Fixes #25416.


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RSS widgets: Omit the title attribute when the summary is shown.

Trim the title attribute to ensure whitespace isn't rendered.

props SergeyBiryukov.
fixes #26520. see #26552.

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Use the current post's post type when determining post adjacency.

props ethitter.
fixes #26937.

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