[ECM] Use ECM allowlists

We recently introduced two SystemConfigManager SystemAPI methods:

    SystemConfigManager::getEnhancedConfirmationTrustedPackages
    SystemConfigManager::getEnhancedConfirmationTrustedInstallers

In this change, we update EnhancedConfirmationService to actually
consume those methods and use them for their intended purpose: as
allowlists.

Bug: 310654834
Test: atest CtsPermissionUiTestCases:android.permissionui.cts.EnhancedConfirmationManagerTest
Change-Id: I67ad1347f306f7c6d4458ccd6849a4ed17783b50