Make formattedPhoneNumber @Nullable

This value could be null, make @Nullable will make sure the generated
SubscriptionInfoDao_Impl will be null safe for formattedPhoneNumber.

Bug: 289155281
Test: m Settings
Test: manual - on Settings Network & internet page
Change-Id: I4e8b1c3d59baaba658d05350b238033775db6aab