Change NetworkFactory to NetworkProvider in telephony.

This is needed to transition from NetworkFactory (which will
not be a public or system API) to NetworkProvider (which is
@SystemApi).

Bug: 138306002
Test: atest FrameworksTelephonyTests, no new failures
Change-Id: I7a662e2cc065e429d5435e81e255d8f1c6603754
Merged-In: I7a662e2cc065e429d5435e81e255d8f1c6603754
Exempt-From-Owner-Approval: already approved by OWNERS as ag/10054133