Expose LocationManager#getNetworkProviderPackage as @SystemApi

The PermissonController is going to become a mainline module, hence it
has to compile against @SystemApi.

The permission controller needs to know which package is the network
provider as it treats the location permission of the location provider
page special.

As far as I understood the current API is not protected. I would like to
leave adding the protection to the location team.

Bug: 110953302
Test: Built
Change-Id: Ic0691bd2254137273160ee6c2e6bb10257205d54