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

.changeset/chilly-zoos-beg.md

@@ -0,0 +1,6 @@
+---
+"@medusajs/dashboard": patch
+"@medusajs/order": patch
+---
+
+fix(dashboard, order): summary pending diff calculation on preview