Update bundled notification guts text to match POR.

This splits out the text for individual bundled notifications and for the bundle header, which need to be different but were previously sharing the same resource string.

Bug: 417257962
Test: manual
Flag: com.android.systemui.notification_bundle_ui
Change-Id: Ic3de2b297d5d82e81d502581c27be7669fe72d9d