Add a getter to get the camera orientation relative to the devices native orientation

[matt-oakes]

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This is useful for when you are using the image data from the onFramePreview callback and need to correct the image rotation before sending it through to something like the Mobile Vision SDK.

The lack of this was causing libraries to make assumptions about the camera orientation which causes bugs like this: https://github.com/react-native-community/react-native-camera/issues/1714

[matt-oakes]

I realised that just after I made this. I've opened a PR over there including both parts https://github.com/react-native-community/react-native-camera/pull/2050