CameraView - Focus and Exposure

[GUOLDEV]

Implement camera controls such as a focus on tap, exposure, etc, like in the MediaPlugin TakePhotoAsync or in the ManualCameraControls as a reference.

Implement camera properties:

• FocusMode;

public CameraFocusMode FocusMode { get; set; }

public enum CameraFocusMode
{
    Locked,
    AutoFocus,
    ContinuousAutoFocus
}

• ExposureMode;

public CameraExposureMode ExposureMode { get; set; }

public enum CameraExposureMode
{
    Locked,
    AutoExpose,
    ContinuousAutoExposure,
    Custom
}

[ashlar64]

I agree. We need many of the features that is found in the MediaPlugin.

[CliffAgius]

Currently being worked on #259