[visualize] fix unsaved state when adding by-value visualize embeddab…

…le to dashboard (elastic#211264)

Follow up to elastic#210125

[8.16](elastic#211057) and
[8.17](elastic#211054) backports for
elastic#210125 were failing functional
test
https://github.com/elastic/kibana/blob/8.17/test/functional/apps/dashboard/group1/dashboard_unsaved_listing.ts#L142.
The functional test adds a by-value and by-reference legacy
visualization to a new dashboard. Upon saving the dashboard, the
dashboard still showed unsaved changes.

The reason this test did not fail main and other branches is that
elastic#208116 removed the "by-value"
part of the test (since its no longer possible to add a by-value legacy
visualization from within a dashboard). It is still possible to recreate
the issue in main with the following steps
1) Click "Visualize Library" in left nav
2) Click "Create visualization" button. 
3) Click "Legacy" tab
4) Click "Aggregation based"
5) Click "Area"
6) Click web logs sample data view
7) Click "Save"
8) Set title
9) Under "Add to dashboard", click "New", click save
10) save dashboard. Notice how dashboard still has unsaved changes.

8.16 and 8.17 required a [new
commit](elastic@1fd631c)
to resolve the issue by updating the `linkedToLibrary` to ignore
undefined values.

This PR fixes the issue for the other branches that have already been
merged.

---------

Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>
Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>

src/platform/plugins/shared/visualizations/public/embeddable/visualize_embeddable.tsx

@@ -308,7 +308,13 @@ export const getVisualizeEmbeddableFactory: (deps: {
           },
         ],
         savedObjectProperties: getUnchangingComparator(),
-        linkedToLibrary: [linkedToLibrary$, (value) => linkedToLibrary$.next(value)],
+        linkedToLibrary: [
+          linkedToLibrary$,
+          (value) => linkedToLibrary$.next(value),
+          (a, b) => {
+            return a === undefined || b === undefined ? true : a === b;
+          },
+        ],
       }
     );