Refactor decision logic out of storage classes (2/2)

To make the storage classes more generic, this CL refactors
RecentPermissionsDecisionStorage to store the more generic
PermissionEvent.

This adds another layer of inheritance/implementation. Previously:

RecentPermissionsDecisionsStorage (client interface)
  RecentPermissionsDecisionStorageImpl (XML db + perm decision logic)

Now:

PermissionEventStorage<T> (client interface)
  BasePermissionEventStorage<T> (XML database logic)
    PermissionDecisionStorageImpl (perm decision logic)

As part of this split, granularity of time storage has been moved to be
an implementation detail of implementations of
BasePermissionEventStorage which changes some of the optimizations around
not storing time changes less than a day.

Bug: 205642821
Test: atest PermissionControllerMockingTests
Change-Id: Ic6a611b93f51a46f7761844aac1ebd8ac22b6c10