Move HUN a11y events to view layer; make sure chip HUNs get announced

Bug: 397507681
Bug: 364653005
Flag: com.android.systemui.notifications_hun_accessibility_refactor

Test: Trigger notification chip then tap on it with TalkBack enabled ->
verify notification content is announced. Tap on chip again -> verify
notification content doesn't re-announce as the HUN disappears

Test: Trigger normal HUN -> verify only notification app name & title is
announced, and then "Swipe with 4 fingers to open" is announced

Test: Trigger 2 notifications chips, tap on one then the other -> verify
second chip gets an a11y announcement

Change-Id: I64ffc4453215a119d991d0f22b1226d4ea2cf29e