Allow gallery_shortcode() and get_image_tag() to accept an array of image dimensions

[johnbillion]

Of all the image-related functions in WordPress that include a $size parameter, almost all of them accept either a registered image size or an array of the image width and height in pixels.

There are three exceptions to this, which do not accept an array:

• gallery_shortcode() ($attr['size'] parameter) because the value gets passed to sanitize_html_class()
• get_image_tag() because the value gets directly used as an HTML attribute
• get_image_send_to_editor() because the value gets passed to get_image_tag()

The gallery_shortcode() and image_tag() functions should be fixed so that they use {$width}x{$height} where the image size is used as an HTML attribute. This is what wp_get_attachment_image() already does when its $size parameter is an array.

The documentation for these functions and their filters are currently incorrect because they state that they do accept either an image name or array of dimensions, therefore this is a backwards-compatible fix.

Related / split from #47364.

[johnbillion]

51362.diff​ fixes these two instances.

[johnbillion]

In 49128:

Media: Allow the gallery_shortcode() and get_image_tag() functions to correctly accept an array of image dimensions.

These functions did previously accept an array of image dimensions but their class attributes were not properly constructed.

Fixes #51362