Add parity between site icon, custom header, and default image crop behaviors. [53027] fixed a bug where alt text and caption were not copied on custom headers, but did not apply that change in any other context.
Deprecate the `create_attachment_object` method in the `Wp_Site_Icon` and `Custom_Image_Header` classes and replace that functionality with the new function `wp_copy_parent_attachment_properties()` to improve consistency.
Props afercia, rcreators, jorbin, joedolson, huzaifaalmesbah, shailu25, swissspidy, mukesh27.
Fixes#60524.
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