Cache StrictMode handle to IStorageManager

Certain StrictMode paths can result in repeated and frequent queries
to IStorageManager.isCeStorageUnlocked. Avoid associated overhead by
caching the IStorageManager handle when necessary.

Note that StorageManager.isCeStorageUnlocked has similar handle caching
behavior. We could simply reuse that method, however, it has slightly
different semantics when the query fails (for StrictMode, we simply
ignore those failures).

Bug: 318403642
Test: presubmit
Change-Id: Ibe52808b314e8f8044d423761d99df680ce2c8e4