Use correct user id to create synthetic path dir

Upon creation, current MediaProvider code is using self user-id as uid
to determine the correct location under which to create
.transforms/synthetic/... path for the user. This is incorrect as user-id is not uid and simply the user-id can be used to
determine the correct path.

Bug: 187544424
Bug: 187544546
Test: atest --user-type secondary_user android.scopedstorage.cts.device.ScopedStorageDeviceTest. Before these
changes the test was failing with secondary_user

Change-Id: I80144fcc131549e5f4a0f5a695b8752034b097b4
1 file changed