Restrict access to directories

Restricted access to Android/data, Android/obb and Android/sandbox
directories and its sub-directories. Replacing path's pattern match
check with file equality check.

Test: atest DocumentsClientTest
Bug: 341680936
Flag: EXEMPT bug fix
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:02c5b768188554188df86ab47416b9cd09b71b5c)
Merged-In: I8879900e57e1702d11797b81e86d0cc3f55bac22
Change-Id: I8879900e57e1702d11797b81e86d0cc3f55bac22