web: clear out selecteds list after an API event to ensure a fresh copy of the policies-to-delete list (#8125)

* web: clear out selecteds list after an API event to ensure a fresh copy of the policies-to-delete list

* Prettier had opinions.

* web: A better fix

This fix creates a new property of Table, 'clearOnRefresh', which
automatically empties the `selectedElements` list when an EVENT_REFRESH
event completes.  Set this flag on any table that uses the
`selectedElements` list for bulk deletion; this ensures that stale
data in the `selectedElements` list will not persist and interfere
with future deletion events.

web/src/admin/blueprints/BlueprintListPage.ts

@@ -58,6 +58,7 @@ export class BlueprintListPage extends TablePage<BlueprintInstance> {
 
     expandable = true;
     checkbox = true;
+    clearOnRefresh = true;
 
     @property()
     order = "name";