Fix storage health check in Cadence 1.0 migration

Currently, storage health check always fails with
"slabs not referenced from account storage" because storage
maps are not loaded in Cadence runtime storage even though
payloads are loaded.

This commit fixes this problem by loading storage map explicitly
after loading payloads in storage.

cmd/util/ledger/migrations/cadence_values_migration.go

@@ -133,6 +133,11 @@ func (m *CadenceBaseMigrator) MigrateAccount(
 			}
 		}
 
+		// Load storage map.
+		for _, domain := range domains {
+			_ = storage.GetStorageMap(address, domain, false)
+		}
+
 		storageHealthErrorBefore = storage.CheckHealth()
 		if storageHealthErrorBefore != nil {
 			m.log.Warn().