Implement the Trashcan Operator

[JasonSteving99]

It's getting a bit old to have to have every single piece of data end up eventually ending up in a print statement due to the fact that all variables must be referenced and that functions/providers cannot be called without referencing their output.

I want a trashcan operator to allow things in the language to go unused, while still being super explicit that they're not used, and also being clear that it's a waste to have things around without using them.

Should look like this:

_ = foo(0);  # throw away the result of this function call.