This simple Kotlin app projects a live feed on the side of a cube.
It looks very similar to the `lit-cube` demo but there is a new Kotlin
class called `CameraHelper` that creates Camera2 objects, starts
the capture session, creates the Filament texture, etc.
For now, this app uses SurfaceTexture. This is a starting point and
provides a testing ground for tentative improvements to our Stream API.
