[WIFI] Open up the getRandomizedMacAddress API

The randomized MAC address needs to be available to DO, PO, and
Carrier apps (which is restricted to getting the randomized MAC
address only from configurations it created).

Unhide the API and document the restrictions.

Bug: 112205095
Test: atest com.android.server.wifi
Test: atest android.net.wifi
Change-Id: I7376a00cf6ada51236d8a00538159e1ca25743b3