Using DiffUtil for calculating widget diff instead
of a custom implementation

This uses the same version as all-apps and avoids whole list refresh
when a widget entry is expanded for the first time

Removing tests which were essentially testing the diffing logic

Bug: 268646258
Test: Verified on device
Change-Id: I4799c66b4674e754547317317e7a63f098fce735
11 files changed