Migrate convertHalCellIdentityToCellIdentity()

Remove convertHalCellIdentityToCellIdentity() in
CellularNetworkService, and introduce create() in CellIdentity
for CellIdentity 1.0 and 1.2.

Bug: 146498725
Test: atest CellularNetworkServiceTest
Change-Id: Icb532113b3a43c7feaab09d73e66caf9671f0b77
Merged-In: Icb532113b3a43c7feaab09d73e66caf9671f0b77
(cherry picked from commit 7ee07046)