A function that gives us access to the [FunctionContext]. All functions have
can accept this context as their first argument. The context is helpful for
several reasons:
A method on a string type. When added to the CEL context, this function
can be called by running. We use the [This] extractor give us a reference
to the string that this method was called on.
A function that illustrates all the different types of values that are supported
as arguments to a function, as well as the fact that any of these types can also
be returned from a function.