Split System category

Splitting System category in
Settings > Storage into "Android 14"
and "Temporary system files".

Android 14 is calculated as
StorageStatsManager#getTotalBytes - (size of /data partition).
Basically it's the size of all partitions
except for the userdata. It also includes
the storage rounding which we do to display
a nice round storage size (128GB, 256GB, etc).

Temporary System Files serves as "Everything else"
category that represents all the used storage
that didn't fall under any other category.
It's the same as how currently "System" category works.

Bug: 309801699
Test: atest StorageItemPreferenceControllerTest
Test: atest StorageCacheHelperTest
Change-Id: Ifae5819bf1d7a1a675df1fa67bd6dcdfa074b584