Media: Accessibility: Add filter for TinyMCE in media descriptions.

Add a filter to enable TinyMCE in the media description textarea on the attachment details screen.

The media description field may be used to provide extended descriptions of images and videos, such as a transcript or detailed graphic explanations. In these uses, it will generally require structural elements like paragraphs. Having the ability to enable TinyMCE makes it easier for users to add this content without HTML knowledge.

Props juliemoynat, sebastienserre, mukesh27, joedolson.
Fixes #60158.
Built from https://develop.svn.wordpress.org/trunk@58372


git-svn-id: http://core.svn.wordpress.org/trunk@57821 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/media.php

@@ -3267,7 +3267,14 @@ function edit_form_image_editor( $post ) {
 		'textarea_name' => 'content',
 		'textarea_rows' => 5,
 		'media_buttons' => false,
-		'tinymce'       => false,
+		/**
+		 * Filter the TinyMCE argument for the media description field on the attachment details screen.
+		 *
+		 * @since 6.6.0
+		 *
+		 * @param bool Activate TinyMCE in media description field. Default false.
+		 */
+		'tinymce'       => apply_filters( 'activate_tinymce_for_media_description', false ),
 		'quicktags'     => $quicktags_settings,
 	);