Remove some read only usages of PackageManagerService mLock

In most non-install, non-mutate areas, migrates away from locking
PackageManagerService directly in favor of the Computer snapshot.

This will relieve more lock contention and allow scoping
PackageSetting to mutate-only scenarios, such as install.

Bug: 202291449

Change-Id: Ie92ebfeacdc4a00484373f11739fdfe3c3897a7f