Update workaround for background widget loading

Instead of removing and re-adding the views, we instead wait for the
view layout to occur and then add the widget as a child view to the
container.

Bug: 356393319
Test: flashed and scrolled through widgets, verified they render
correctly
Flag: com.android.systemui.communal_hub

Change-Id: I1f522cebbaf7561cfbfb00c57af64dea386a2605