[Font API] Use registered fonts for Block Editor iframe. (#49646)

* Use queue for Site Editor

* Capture site editor check in variable.

To capture the site editor identification condition in one place.

Why?

To improve readability and maintability, especially if the identification
logic changes in the future.

lib/compat/wordpress-6.2/script-loader.php

@@ -130,26 +130,33 @@ function gutenberg_resolve_assets_override() {
 	$scripts = ob_get_clean();
 
 	/*
-	 * Generate font @font-face styles for the site editor iframe.
-	 * Use the registered font families for printing.
+	 * Generate font @font-face styles for the iframe.
+	 *
+	 * For the Site Editor, use the registered fonts.
+	 * For the Block Editor, use the enqueued fonts.
 	 */
 	if ( class_exists( 'WP_Fonts' ) ) {
-		$wp_fonts   = wp_fonts();
-		$registered = $wp_fonts->get_registered_font_families();
-		if ( ! empty( $registered ) ) {
-			$queue = $wp_fonts->queue;
-			$done  = $wp_fonts->done;
+		$wp_fonts       = wp_fonts();
+		$registered     = $wp_fonts->get_registered_font_families();
+		$is_site_editor = 'site-editor.php' === $pagenow;
 
-			$wp_fonts->done  = array();
-			$wp_fonts->queue = $registered;
+		if ( ! empty( $registered ) ) {
+			$done           = $wp_fonts->done;
+			$wp_fonts->done = array();
+			if ( $is_site_editor ) {
+				$queue           = $wp_fonts->queue;
+				$wp_fonts->queue = $registered;
+			}
 
 			ob_start();
 			$wp_fonts->do_items();
 			$styles .= ob_get_clean();
 
-			// Reset the Web Fonts API.
-			$wp_fonts->done  = $done;
-			$wp_fonts->queue = $queue;
+			// Reset the Fonts API.
+			$wp_fonts->done = $done;
+			if ( $is_site_editor ) {
+				$wp_fonts->queue = $queue;
+			}
 		}
 	}