[DataStore] Provide BackupRestoreFileStorage

Bug: 325144964
Test: Manual tests
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:50784fe9c08b868ec04562f7ae3df751515c9ee3)
Merged-In: I9ad13305321d0c9f5f6dccc46c266443fd45f73e
Change-Id: I9ad13305321d0c9f5f6dccc46c266443fd45f73e
4 files changed