Fix PowerStats.Descriptor.extras comparison

Without this fix, two descriptors are seen as different
if they contain any arrays (e.g. screen and sensors)

Bug: 395954049
Test: atest PowerStatsTests; atest PowerStatsTests:BatteryUsageStatsProviderPerfTest#getBatteryUsageStats_accumulated
Flag: EXEMPT bugfix
Change-Id: Ic027a6f47538e4cb0bbd33555996b93f19218c71