[Notif redesign] Show title in legacy messaging notifs

Previously, we were collapsing the title into the top line when a legacy
messaging notification was being expanded. Now we're showing it
normally, as we do for other styles incl. the new conversation layout.

Test: manual + screenshot tests
Flag: android.app.notifications_redesign_templates
Bug: 378660052
Change-Id: I68b3d749c2927ca6810a979c1ef61660fdba0f9e