Query storage size instead of calculate size of installed APP

From android S, Storage Settings show files of images/videos/audios
category instead of installed APP of each category. So it's
necessary to change the way to calculate size information.

This change also
- StorageItemPreference shows changing storage size units instead
  of fixed GB. It helps UX for categories of only small size files.
- Query media provider for size of Documents and others.
- Query media provider for size of Trash.

Bug: 170918505
Bug: 177892478
Bug: 179871408
Bug: 184379946
Bug: 186077224
Bug: 187128447
Test: atest com.android.settings.deviceinfo
      atest com.android.settings.deviceinfo.storage
      make RunSettingsRoboTests -j ROBOTEST_FILTER=com.android.settings.deviceinfo
      make RunSettingsRoboTests -j ROBOTEST_FILTER=com.android.settings.deviceinfo.storage
      manual visual
      Click each file category to count files size is the same as
      displayed in Storage Settings.
Change-Id: I37c7b3a4b5860323cb55581b23a90f583f4af216