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: Ibf07f770b377c383ea0c4d3ef2d1d991a37854a9
Merged-In: Ibf07f770b377c383ea0c4d3ef2d1d991a37854a9
(cherry picked from commit f55983a5)