Add USSD codes over IMS feature

Add config to allow USSD over IMS.
If it is not supported due to modem limitations, USSD send over the CS
pipe instead.

Test: atest ImsPhoneTest
Bug: 141350403
Merged-In: If0cc0aecd9d9a321715a15c83b9e8473eb1ae91d
Change-Id: If0cc0aecd9d9a321715a15c83b9e8473eb1ae91d
(cherry picked from commit 307db944)