Ensure that NotificationStackAppearanceViewBinder updates happen synchronously on the main thread

Note: this doesn't fully fix the frame delay for scroll position updates, but is required.

Bug: 325467496
Test: atest SystemUITests
Flag: ACONFIG com.android.systemui.scene_container DEVELOPMENT
Change-Id: Ieebf0ee27a090f3bf11a2f0355f1b384d3746c6e