WP_Image_Editor: inline documentation fixed for multi_resize array keys

[paolal]

Added mention that:

	 * The key of each array will be returned as the image size (generally 'small', 'medium', or 'large').

and updated example:

	 * @param array $sizes { ['size'] => {'width'=>int, 'height'=>int, ['crop'=>bool]}, ... }

to remind that even if the key is not required, it has to be returned by the function due to core's utilisation of multi_resize

Seen with @DH-Shredder

[markoheijnen]

looks great and ready to commit.

[DrewAPicture]

Array parameters should be documented using the ​hash notation style outlined in the inline docs standards.

[DrewAPicture]

hash notations

[DrewAPicture]

25530.2.diff​ handles the array hash notations.

[DrewAPicture]

In 25728:

Improve inline documentation for the multi_resize() method in WP_Image_Editor, WP_Image_Editor_GD, and WP_Image_Editor_Imagick.

Props paolal for the initial patch.
Fixes #25530.