(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).
We should probably update the comments above here (i.e. `@param (type,name) [Symbol]...`) to reflect the String -> Symbol change.