Camera: Improve logical camera RAW capture docs

- Clarify raw capture behavior for logical camera with backward
compatible approach and MultiResolutionImageReader.
- Some logical camera devices may have identical physical cameras with
different focal length. Allow such logical camera to switch physical
cameras when outputing raw.

Bug: 182217158
Test: Build
Change-Id: I64458683f4eb8be6fc1e35270a8c22864d962be9