"Hide" /Android/data|obb|sanbox/ on shared storage

Implement shouldHideDocument() in the ExternalStorageProvider so that it
resitcts access to 'Android/data/', 'Android/obb/' and 'Android/sandbox'
on the integrated shared storage along with all their content and
subdirectories.

Clean up the abstract FileSystemProvider, specifically all variants of
queryChildDocuments().

Bug: 200034476
Bug: 220066255
Bug: 283962634
Test: make & flash systemimage, run manually
Test: atest ExternalStorageProviderTests
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:7f5667bfafbd9b1b4d59c2cb15f9a3e07a559318)
Merged-In: I48c2ce7ff2d7fc067961ea2af0ea63818316f086
Change-Id: I48c2ce7ff2d7fc067961ea2af0ea63818316f086