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
2 files changed