(PUP-2904) Make functions 4 API require symbol param names

There was a mix of String and Symbol in our code. This enforces
that parameter names must be Symbol. Thus it is up to the caller to
use the right thing as this is better than performing an intern
(performance and may intern something big/bad).
(PUP-2904) Correct documented type of the name param

The documented type of the parameter name in the param method
was still showing 'String' when it is now required to be a Symbol.

This commit corrects the documentation comment.
Merge pull request #3360 from hlindberg/PUP-2904_consistent-func-api-wrt-param-names

(PUP-2904) Make functions 4 API require symbol param names