Adding input example project

[acianrice]

As requested by Adrian, this is a small example projected of using different inputs on the glasses (back gesture, generic motion inputs, and the camera action). Not sure if this is exactly what folks were looking for.

[snippet-bot]

Here is the summary of changes.

You are about to add 4 region tags.

• xr/src/main/java/com/example/xr/input/app/src/main/java/com/example/aiglasses/camera/HelloBackGestureActivity.kt:15, tag androidxr_projected_back_gesture_callback
• xr/src/main/java/com/example/xr/input/app/src/main/java/com/example/aiglasses/camera/HelloBackGestureActivity.kt:27, tag androidxr_projected_back_gesture_register
• xr/src/main/java/com/example/xr/input/app/src/main/java/com/example/aiglasses/camera/HelloCameraActionActivity.kt:44, tag androidxr_projected_camera_action_observe
• xr/src/main/java/com/example/xr/input/app/src/main/java/com/example/aiglasses/camera/HelloMotionGestureActivity.kt:29, tag androidxr_projected_motion_gesture_dispatch

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[google-cla]

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[trambui09]

Hi @acianrice, since this is your first time contributing, please make sure to sign the google CLA.

This PR contains a lot of boilerplate code. I would suggest distilling it down to the minimum code needed for the snippets. See https://github.com/android/snippets/tree/main/xr/src/main/java/com/example/xr for some examples. This will help with maintenance.