perf: improve performance of SharedStorage::getWatcher #14665

Job	Run time
changes	7s
integration-sqlite (capabilities_features, 8.1, main)	1m 43s
integration-sqlite (collaboration_features, 8.1, main)	2m 45s
integration-sqlite (comments_features, 8.1, main)	2m 10s
integration-sqlite (dav_features, 8.1, main)	5m 47s
integration-sqlite (features, 8.1, main)	6m 40s
integration-sqlite (federation_features, 8.1, main)	2m 42s
integration-sqlite (--tags ~@large files_features, 8.1, main)	6m 39s
integration-sqlite (filesdrop_features, 8.1, main)	1m 37s
integration-sqlite (openldap_features, 8.1, main)	1m 34s
integration-sqlite (openldap_numerical_features, 8.1, main)	1m 40s
integration-sqlite (ldap_features, 8.1, main)	1m 27s
integration-sqlite (remoteapi_features, 8.1, main)	1m 32s
integration-sqlite (setup_features, 8.1, main)	1m 35s
integration-sqlite (sharees_features, 8.1, main)	3m 20s
integration-sqlite (sharing_features, 8.1, main)	6m 40s
integration-sqlite (videoverification_features, 8.1, main)	4m 14s
integration-sqlite-summary	4s
	52m 16s

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