Simplifying pending widget inflation path

Instead of adding a PendingView in appWidgetHost, attaching a
listener in PendingView for widget-updates.

This moves the view inflation as the last stage of widget
binding. Eventually we can separate the model update and view
inflation to different threads

Bug: 318539160
Test: atest TaplBinderTests
Flag: None
Change-Id: I124edaa9622fa367302b80969036d128a978396e