Properly store device policy user restrictions.

Bug: 299302474
Bug: 311687929
Test: btest "android.devicepolicy.cts.UserRestrictionsTest" && atest UserManagerServiceUserInfoTest#testWriteReadDevicePolicyUserRestrictions

(cherry picked from commit 24202a9b)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:c747c3fd1a0111eb699b950e645080470f0cead8)
Merged-In: I66159f362b45d4c9e322754ff272c373b2557812
Change-Id: I66159f362b45d4c9e322754ff272c373b2557812