Return the path events for rendering as an Option, so that if the path is empty,
we simply return.
This avoids a double property dependency in the (likely) event the path is not empty.
The crate is an internal crate until the API has been polished and
documented, after which we can call slint-renderer-skia for example.
This also duplicates a little bit of the glutin setup code, because
that would otherwise have to go into another shared crate.
