Support MockModem for secondary users

The CL fixes the MockModem connection failure in HSUM by switching from
bindService to bindServiceAsUser API call.

bindService works only for system user. For secondary users, calling
bindService to bind MockModem service will make the service invisible
for secondary users (including main user) and fail the connection.

The issue is fixed by calling bindServiceAsUser and passing current
user to make sure the MockModem service is launched and bound for the current user.

Bug: 353531688
Test: MockModem CTS tests with both HSUM on and off
Flag: com.android.internal.telephony.flags.support_phone_uid_check_for_multiuser
Change-Id: I3ffdb90b8a9692929c7abc1a21916ea1c4cd0800