Fix Atom Shell from always using the discrete GPU

While the `NSSupportsAutomaticGraphicsSwitching` attribute was added to [atom/browser/resources/mac/Info.plist](https://github.com/atom/atom-shell/blob/05216630765a52b8f3115cf288530b6729ba5323/atom/browser/resources/mac/Info.plist#L19-20), it was missing from Info.plist files in `renderer/` and `common/`. This was causing Atom Helper.app to not have this attribute, which in turn causes the discrete GPU to become active.