[flexiglass] basic impl of ActivityStarterInternal

Basic activity starter functionality works when there's no
security set (SWIPE or NONE).

Alternate bouncer shows from lockscreen but is still broken
from the notification shade due to KTF transitioning from
lockscreen => undefined instead of lockscreen => shade.

Primary bouncer shows from the lockscreen but the intent
doesn't launch after successful auth.

Test: startActivity(): tap on settings icon from the shade
when the device is unlocked.
Test: dismissKeyguardThenExecute(): tap on a notification from
the lockscreen (with or without fingerprint enrolled), user can
authenticate to proceed to notification intent
Test: startPendingIntentDismissingKeyguard(): tap on a smart
reply (currently only works from unlocked home screen)
Bug: 308819693
Flag: com.android.systemui.scene_container

Change-Id: If5b65833082306edcecccc66b265df541769fd5c