Update lockscreen detection

keyguard_clock_container is being removed. The
keyguard_indication_area should be a reasonable replacement in order
to detect lockscreen visibility.

Allow platform tests and libraries to use SystemUI flags.

Test: atest PlatformScenarioTests
Fixes: 325325938
Flag: ACONFIG com.android.systemui.migrate_clocks_to_blueprint
DEVELOPMENT

Change-Id: Ib8927c57c24ae83b4e747d06b91ab6e2ed3e51a2