Implement foreach to iterate over system properties
The API client will receive system properties that it is allowed to get
by sepolicy.
Bug: 231969630
Test: Use in an Android process. Print names and values. See those
properties allowed by sepoicy.
Change-Id: Ib2c30e6c2e58eb048cae275187acd1f74a8de577
Merged-In: Ib2c30e6c2e58eb048cae275187acd1f74a8de577