Leverage new Kotlin AutoCloseable Interface

[ccjernigan]

Is your feature request related to a problem? Please describe.

As part of #158, an internal Closeable interface was added. This interface is deprecated by design, as it will be replaced by a Kotlin language feature

Describe the solution you'd like

Once the Kotlin Closeable interface is stable (doesn't require an opt-in annotation), we should leverage it instead of our own interface.