* Initial steps on GPU printing example

This change is checkpointing work on a new Slang example that shows how a "GPU `printf()`" can be implemented almost entirely in user space thanks to a combination of Slang language and API features.

The example is not perfect as it stands today due to limitations in our current handling of hashed string literals:

* At call sites where a string literal is passed, we currently have to explicitly invoke `getStringHash()` to get the hash code, because we don't currently support `String` as a function argument/parameter type.

* On the implementation side, because strings are passed as their `int` hash codes, we can't tell them apart from ordinary `int` arguments. The current code handles this by assuming an `int` is *always* a hashed string, which obviously isn't appropriate.

There are plenty of other limitations in the implementation presented, but the above are the two main things I'd like to address in follow-up work.
I would like to checkpoint this work on the application first, in order to keep work on the Slang implementation and the example as separate as possible.

* typo