camera2-portability: Switch to ratio-based zoom interfaces

This eliminates the deprecated index-based CameraSettings zoom methods in favor
of floating-point ratio based versions, and includes the plumbing to make those
work for both the camera1 and camera2 underlying framework APIs.

Bug: 17016658
Change-Id: I0567a53cd57bfa6d53604e3c5457a39ef49e3cb4