Implement SafetyCenterIssueRepository.

This class will keep SafetyCenter issues up-to-date, including
performing deduplication and issue sorting on each state update.

Along with this, we move 2 methods that don't deal with dismissals from
SafetyCenterIssueDismissalRepository, so we can name it this way.

Test: atest CtsSafetyCenterTestCases
Test: atest SafetyCenterFunctionalTestCases
Bug: 264849615
Bug: 264850687
Bug: 266555164
Change-Id: Iaf577a04ea924e82c1f2fa12046c20428c1a9290