Setup interface for ActivityStarterInternal

To separate flexiglass enabled logic from when
flexiglass is not enabled.

Flag: ACONFIG com.android.systemui.scene_container DEVELOPMENT
Test: builds, no changes, intents launch normally w/o flag enabled
Test: atest LegacyActivityStarterInternalImplTest
Bug: 308819693
Change-Id: I7db3eadc3e201b47658aa9ef45c19044adbe68ae
6 files changed