Add equality method for PhoneAccount.

Checks for equality between two PhoneAccounts, not taking into account
the icon, which cannot be compared with equality.

Test: Manual as part of telephony account registry updates.
Test: Added new unit tests to test equality.
Bug: 112884689
Merged-In: Change-Id: Ibd0c69425bf185dc6b79db4ca4e9ca4a770320a3
Change-Id: Ibd0c69425bf185dc6b79db4ca4e9ca4a770320a3
(cherry picked from commit a04bd3d2)