fix: insertion marker's next blocks become real block (#7384)

Don't add next block to the insertion marker when we do
an insertion marker json serialization.

Also, to keep consistent with the old behavior, we don't
need to add input blocks for the insertion marker.

And we don't need to do a full serialization here as it
will just become an insertion marker.

Resolves #7383

Address issues in PR #7364

Signed-off-by: Hollow Man <[email protected]>

core/insertion_marker_manager.ts

@@ -225,7 +225,12 @@ export class InsertionMarkerManager {
     eventUtils.disable();
     let result: BlockSvg;
     try {
-      const blockJson = blocks.save(sourceBlock);
+      const blockJson = blocks.save(sourceBlock, {
+        addCoordinates: false,
+        addInputBlocks: false,
+        addNextBlocks: false,
+        doFullSerialization: false,
+      });
       if (!blockJson) {
         throw new Error('Failed to serialize source block.');
       }