Add has_image_size()

[mordauk]

The remove_image_size() function is proposed as being introduced in #26768.

​markoheijnen suggested that has_image_size() also be added.

I can recall a few scenarios when I've needed to check if an image size exists, so I'm all for it.

[mordauk]

Adds has_image_size()

[mordauk]

Unit tests for this (also add_image_size() and remove_image_size()) added in ticket:26768:26768-tests.patch​ on #26768

[wonderboymusic]

In 27128:

Introduce has_image_size( $name ), a utility function that helps avoid loading the $_wp_additional_image_sizes global.

Props mordauk.
Fixes #26951.

[nacin]

In 27129:

Add remove_image_size() and tests for it and has_image_size(), added in [27128].

props mordauk, markoheijnen.
fixes #26768. see #26951.

[mordauk]

Thanks guys!

[DrewAPicture]

In 27139:

Inline documentation tweaks for has_image_size() and remove_image_size().

See #26951.

[nacin]

In 27140:

has_image_size()'s parameter should be required. see [27139], see #26951.