Init and show bundle header and set ENR on entry

When ENR is not set on entry it causes NPEs downstream. Setting it here
right after the row is created and known seems appropriate.

We want to create the ViewModel from dagger such that we can easily
inject other objects.

Test: manual test bundle (not bugfree yet)
Flag: com.android.systemui.notification_bundle_ui
Bug: b/389839492
Change-Id: I4503d00f49b5a422d50edf5398f8aaede2b2d14a