Aidl changes related to VideoCallProvider in Ims.

+ Added a getVideoCallProvider function in IImsCallSession
+ Added IImsVideoCallProvider aidl. This is used for communication
between Telephony and the ImsService. It is redundant with
IVideoCallProvider on some level, but see associated bug and comments
in the class for more detail.
+ Added IImsVideoCallCallback. This is used for communicationing
callback invocations from ImsService to Telephony. It is redundant
with IVideoCallCallback for same reason in bugs/comments.
+ Some minor formatting changes.

Bug: 16886403
Change-Id: I03de12d4432f837e0930bc077307509b645493e0