Merge BundleHeader guts accessibility node & add a long click handler

This makes the guts selectable, with a long-click action both announced and available to be performed via accessibility action if needed. This essentially reproduces the AccessibilityDelegate added to other non-Compose notification guts views.

Fixes: 432285241
Test: manual by interacting with guts via both TalkBack and Voice Access
Flag: com.android.systemui.notification_bundle_ui
Change-Id: Ib5e54ba5e081f027737baa7c794d909908f537d1