feat: preview library block changes in course unit [FC-0062] (#1506)

Creates a new preview library block modal. Intercepts the message when the block is iframed to open the new modal.

src/course-unit/CourseUnit.test.jsx

@@ -102,6 +102,9 @@ jest.mock('@tanstack/react-query', () => ({
   useQueryClient: jest.fn(() => ({
     setQueryData: jest.fn(),
   })),
+  useMutation: jest.fn(() => ({
+    mutateAsync: jest.fn(),
+  })),
 }));
 
 const clipboardBroadcastChannelMock = {