Revert "Don't force iframe editor when gutenberg plugin and block theme are enabled (#65372)"

This reverts commit 99fefd7.

Author: t-hamano

packages/edit-post/src/components/layout/use-should-iframe.js

@@ -6,22 +6,33 @@ import { useSelect } from '@wordpress/data';
 import { store as blocksStore } from '@wordpress/blocks';
 import { store as blockEditorStore } from '@wordpress/block-editor';
 
+const isGutenbergPlugin = globalThis.IS_GUTENBERG_PLUGIN ? true : false;
+
 export function useShouldIframe() {
-	const { hasV3BlocksOnly, isEditingTemplate, isZoomOutMode } = useSelect(
-		( select ) => {
-			const { getCurrentPostType } = select( editorStore );
-			const { __unstableGetEditorMode } = select( blockEditorStore );
-			const { getBlockTypes } = select( blocksStore );
-			return {
-				hasV3BlocksOnly: getBlockTypes().every( ( type ) => {
-					return type.apiVersion >= 3;
-				} ),
-				isEditingTemplate: getCurrentPostType() === 'wp_template',
-				isZoomOutMode: __unstableGetEditorMode() === 'zoom-out',
-			};
-		},
-		[]
-	);
+	const {
+		isBlockBasedTheme,
+		hasV3BlocksOnly,
+		isEditingTemplate,
+		isZoomOutMode,
+	} = useSelect( ( select ) => {
+		const { getEditorSettings, getCurrentPostType } = select( editorStore );
+		const { __unstableGetEditorMode } = select( blockEditorStore );
+		const { getBlockTypes } = select( blocksStore );
+		const editorSettings = getEditorSettings();
+		return {
+			isBlockBasedTheme: editorSettings.__unstableIsBlockBasedTheme,
+			hasV3BlocksOnly: getBlockTypes().every( ( type ) => {
+				return type.apiVersion >= 3;
+			} ),
+			isEditingTemplate: getCurrentPostType() === 'wp_template',
+			isZoomOutMode: __unstableGetEditorMode() === 'zoom-out',
+		};
+	}, [] );
 
-	return hasV3BlocksOnly || isEditingTemplate || isZoomOutMode;
+	return (
+		hasV3BlocksOnly ||
+		( isGutenbergPlugin && isBlockBasedTheme ) ||
+		isEditingTemplate ||
+		isZoomOutMode
+	);
 }