Customizer: Remove Widgets panel when a theme does not support widgets

By setting 'theme_supports' on the panel, we ensure that the Widgets panel is
removed if a theme does not have support for 'widgets'.

This makes the behaviour of the Widgets and Menus panels consistent.

Follows [52621].
See #54888.
Props hellofromTonya, costdev, peterwilsoncc.

Built from https://develop.svn.wordpress.org/trunk@52622


git-svn-id: http://core.svn.wordpress.org/trunk@52210 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-wp-customize-widgets.php

@@ -420,6 +420,7 @@ final class WP_Customize_Widgets {
 				'priority'                 => 110,
 				'active_callback'          => array( $this, 'is_panel_active' ),
 				'auto_expand_sole_section' => true,
+				'theme_supports'           => 'widgets',
 			)
 		);
 

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.0-alpha-52621';
+$wp_version = '6.0-alpha-52622';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.