Docs: Add missing documentation for some Customize class properties:

* `WP_Customize_Background_Image_Control::$type`
* `WP_Customize_Background_Image_Setting::$id`
* `WP_Customize_Header_Image_Setting::$id`

Follow-up to [21037], [21053], [30885].

Props iamjaydip.
See #55646.
Built from https://develop.svn.wordpress.org/trunk@53411


git-svn-id: http://core.svn.wordpress.org/trunk@53000 1a063a9b-81f0-0310-95a4-ce76da25c4cd

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

@@ -15,6 +15,13 @@
  * @see WP_Customize_Image_Control
  */
 class WP_Customize_Background_Image_Control extends WP_Customize_Image_Control {
+
+	/**
+	 * Customize control type.
+	 *
+	 * @since 4.1.0
+	 * @var string
+	 */
 	public $type = 'background';
 
 	/**

wp-includes/customize/class-wp-customize-background-image-setting.php

@@ -15,6 +15,13 @@
  * @see WP_Customize_Setting
  */
 final class WP_Customize_Background_Image_Setting extends WP_Customize_Setting {
+
+	/**
+	 * Unique string identifier for the setting.
+	 *
+	 * @since 3.4.0
+	 * @var string
+	 */
 	public $id = 'background_image_thumb';
 
 	/**

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

@@ -15,6 +15,7 @@
  * @see WP_Customize_Image_Control
  */
 class WP_Customize_Header_Image_Control extends WP_Customize_Image_Control {
+
 	/**
 	 * Customize control type.
 	 *

wp-includes/customize/class-wp-customize-header-image-setting.php

@@ -17,6 +17,13 @@
  * @see WP_Customize_Setting
  */
 final class WP_Customize_Header_Image_Setting extends WP_Customize_Setting {
+
+	/**
+	 * Unique string identifier for the setting.
+	 *
+	 * @since 3.4.0
+	 * @var string
+	 */
 	public $id = 'header_image_data';
 
 	/**

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.1-alpha-53410';
+$wp_version = '6.1-alpha-53411';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.