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.

Test: Build
Bug: 182217158
Change-Id: I74c4be01c268301df1fd59f6115c36e02fc6a2fe