fix(dashboard,order): preview pending diff summary (#14221)

* wip: preview pending diff summary

* fix: return test

* fix: rm return calc from processAction_

* chore: cleanup

* chore: changeset

* feat: add estimated diff for return,claim,exchange forms

* chore: changeset

integration-tests/http/__tests__/returns/returns.spec.ts

@@ -482,7 +482,7 @@ medusaIntegrationTestRunner({
           expect.objectContaining({
             transaction_total: 0,
             current_order_total: 61,
-            pending_difference: 11,
+            pending_difference: 61, // item is not yet received
             paid_total: 0,
             refunded_total: 0,
           })
@@ -710,6 +710,12 @@ medusaIntegrationTestRunner({
           })
         )
 
+        expect(result.data.order_preview.summary).toEqual(
+          expect.objectContaining({
+            pending_difference: 61 + 1002, // original total + newly added shipping
+          })
+        )
+
         result = await api.post(
           `/admin/returns/${returnId}/request`,
           {},