The `wp_get_loading_optimization_attributes()` function was introduced in 6.3, as a single centralized place to control loading optimization attributes for various tags, most importantly images.
This changeset consolidates the `decoding="async"` optimization, which was added in 6.1, to occur solely as part of `wp_get_loading_optimization_attributes()`, removing duplicate code and allowing centralized filtering based on [56651].
As part of the change, the `wp_img_tag_add_decoding_attr()` function has been deprecated. The filter of the same name continues to be maintained for backward compatibility, as before covering only images that are part of a content blob such as post content (`the_content`).
Props pereirinha, mukesh27, joemcgill, flixos90.
Fixes#58892.
See #53232.
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