Docs: Add documentation for `header_video_settings` filter.

Props milana_cap.
Fixes #43300.

git-svn-id: https://develop.svn.wordpress.org/trunk@42707 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/theme.php

@@ -1467,6 +1467,13 @@ function get_header_video_settings() {
 		$settings['mimeType'] = $video_type['type'];
 	}
 
+	/**
+	 * Filters header video settings.
+	 *
+	 * @since 4.7.0
+	 *
+	 * @param array $settings An array of header video settings.
+	 */
 	return apply_filters( 'header_video_settings', $settings );
 }