Carousel: disable WordPress Core' Lightbox option (#36565)

Fixes #32668

It's best to keep only one lightbox option, to avoid any confusion. Since Jetpack's Carousel feature currently offers more features, let's keep ours in favor of Core's for now.
In the future, when core's lightbox option becomes more robust, we can consider deprecating Jetpack's Carousel feature altogether.

projects/plugins/jetpack/changelog/fix-carousel-lightbox-disable

@@ -0,0 +1,4 @@
+Significance: patch
+Type: compat
+
+Carousel: disable WordPress' lightbox option when Jetpack's Carousel feature is activated.

projects/plugins/jetpack/modules/carousel/jetpack-carousel.php

@@ -83,6 +83,9 @@ public function init() {
 		$this->single_image_gallery_enabled            = ! $this->maybe_disable_jp_carousel_single_images();
 		$this->single_image_gallery_enabled_media_file = $this->maybe_enable_jp_carousel_single_images_media_file();
 
+		// Disable core lightbox when Carousel is enabled.
+		add_action( 'wp_theme_json_data_theme', array( $this, 'disable_core_lightbox' ) );
+
 		if ( is_admin() ) {
 			// Register the Carousel-related related settings.
 			add_action( 'admin_init', array( $this, 'register_settings' ), 5 );
@@ -206,6 +209,32 @@ public function maybe_enable_jp_carousel_single_images_media_file() {
 		return apply_filters( 'jp_carousel_load_for_images_linked_to_file', false );
 	}
 
+	/**
+	 * Disable the "Lightbox" option offered in WordPress core
+	 * whenever Jetpack's Carousel feature is enabled.
+	 *
+	 * @since $$next-version$$
+	 *
+	 * @param WP_Theme_JSON_Data $theme_json Class to access and update theme.json data.
+	 */
+	public function disable_core_lightbox( $theme_json ) {
+		return $theme_json->update_with(
+			array(
+				'version'  => 2,
+				'settings' => array(
+					'blocks' => array(
+						'core/image' => array(
+							'lightbox' => array(
+								'allowEditing' => false,
+								'enabled'      => false,
+							),
+						),
+					),
+				),
+			)
+		);
+	}
+
 	/**
 	 * Returns the value of the applied jp_carousel_asset_version filter
 	 *