Docs: Add documentation for the $type and $mime_type properties in WP_Customize_Image_Control.

Follow-up to [20319], [30309], [31698], [32023], [49679].

Props subrataemfluence.
Fixes #44411.

git-svn-id: https://develop.svn.wordpress.org/trunk@49680 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/customize/class-wp-customize-image-control.php

@@ -15,7 +15,20 @@
  * @see WP_Customize_Upload_Control
  */
 class WP_Customize_Image_Control extends WP_Customize_Upload_Control {
-	public $type      = 'image';
+	/**
+	 * Control type.
+	 *
+	 * @since 3.4.0
+	 * @var string
+	 */
+	public $type = 'image';
+
+	/**
+	 * Media control mime type.
+	 *
+	 * @since 4.1.0
+	 * @var string
+	 */
 	public $mime_type = 'image';
 
 	/**