fix: refresh xblock inline after accepting/rejecting library sync (#2022) (#2028)

Instead of reloading the entire Unit after syncing changes from the
library, just reload the xblock that was changed.

(cherry picked from commit ac5574d)

Author: pomegranited

src/course-unit/preview-changes/index.test.tsx

@@ -85,7 +85,10 @@ describe('<IframePreviewLibraryXBlockChanges />', () => {
     const acceptBtn = await screen.findByRole('button', { name: 'Accept changes' });
     userEvent.click(acceptBtn);
     await waitFor(() => {
-      expect(mockSendMessageToIframe).toHaveBeenCalledWith(messageTypes.refreshXBlock, null);
+      expect(mockSendMessageToIframe).toHaveBeenCalledWith(
+        messageTypes.completeXBlockEditing,
+        { locator: usageKey },
+      );
       expect(axiosMock.history.post.length).toEqual(1);
       expect(axiosMock.history.post[0].url).toEqual(libraryBlockChangesUrl(usageKey));
     });
@@ -100,7 +103,6 @@ describe('<IframePreviewLibraryXBlockChanges />', () => {
     const acceptBtn = await screen.findByRole('button', { name: 'Accept changes' });
     userEvent.click(acceptBtn);
     await waitFor(() => {
-      expect(mockSendMessageToIframe).not.toHaveBeenCalledWith(messageTypes.refreshXBlock, null);
       expect(axiosMock.history.post.length).toEqual(1);
       expect(axiosMock.history.post[0].url).toEqual(libraryBlockChangesUrl(usageKey));
     });
@@ -118,7 +120,10 @@ describe('<IframePreviewLibraryXBlockChanges />', () => {
     const ignoreConfirmBtn = await screen.findByRole('button', { name: 'Ignore' });
     userEvent.click(ignoreConfirmBtn);
     await waitFor(() => {
-      expect(mockSendMessageToIframe).toHaveBeenCalledWith(messageTypes.refreshXBlock, null);
+      expect(mockSendMessageToIframe).toHaveBeenCalledWith(
+        messageTypes.completeXBlockEditing,
+        { locator: usageKey },
+      );
       expect(axiosMock.history.delete.length).toEqual(1);
       expect(axiosMock.history.delete[0].url).toEqual(libraryBlockChangesUrl(usageKey));
     });

src/course-unit/preview-changes/index.tsx

@@ -180,12 +180,14 @@ const IframePreviewLibraryXBlockChanges = () => {
     return null;
   }
 
+  const blockPayload = { locator: blockData.downstreamBlockId };
+
   return (
     <PreviewLibraryXBlockChanges
       blockData={blockData}
       isModalOpen={isModalOpen}
       closeModal={closeModal}
-      postChange={() => sendMessageToIframe(messageTypes.refreshXBlock, null)}
+      postChange={() => sendMessageToIframe(messageTypes.completeXBlockEditing, blockPayload)}
     />
   );
 };