Make SettingsProvider able to restoreAnyVersion, but only

for supported keys

RestoreAnyVersion is supported only for K/V, as full backup
of SettingsProvider has been deprecated (b/71746093).
The supported keys whitelist only contains KEY_WIFI_NEW_CONFIG
and KEY_NETWORK_POLICIES for now, and will be extended in future CLs.

Bug: 64988620
Test: manual (P->P - master without changes to master with changes)
Test: manual (Q->P = API29 -> API28)
Test: a lot of other scenarios covered by our end-to-end tests
Change-Id: I381617b5db9a33b24d400945cffbc59db78ebbd2