Fix getWidgetItemSizePx estimation

The size returned by getWidgetItemSizePx is used by the widget picker
for the NavigableAppWidgetHostView. We should NOT deduct the padding
applied to NavigableAppWidgetHostView to this size.

If a launcher grid insets NavigableAppWidgetHostView, then we must
add the inset to the NavigableAppWidgetHostView width / height.

Test: Compare the size of widgets in preview and home screen using
      layout inspector. See screenshots in the bug
Fix: 200983939
Change-Id: I35022861b65f2624f69940cf3856d9c47f8dbbd9