Replace ListEntry/GroupEntry with PipelineEntry

Add methods to PipelineEntry currently called on
ListEntry and NotificationEntry

Add instanceof checks for GroupEntry-specific logic

Provide empty implementations in BundleEntry

Bug: 394483200
Test: build and use notifications normally
Flag: com.android.systemui.notification_bundle_ui
Change-Id: Ib39edfa37698edd8fee96c2fb3d3376532349a56