[camera_android] Add support to manipulate focus distance and focus mode manually


## Use case
in https://pub.dev/packages/camera
I need to manipulate focus distance manually 
specifically this feature --
set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_OFF)
set(CaptureRequest.LENS_FOCUS_DISTANCE, value)
these methods are available on android camera2 for CaptureRequest.Builder

thanks in advance