Use PlatformConfig to gate behavior

This change moves away from AppOps and explicit targetSdk
checks in favor of PlatformConfig.

Test: atest AppsFilterTest
Test: adb shell device_config put package_manager_service package_query_filtering_enabled true && atest AppEnumerationTests
Fixes: 139348423
Bug: 136675067
Change-Id: If0af198c86210c05c2e10b71f7ae6dc0b7a3ea9a