Parse the rest of one or more argument expressions.
(parse-argument-expressions-rest prev-exprs prev-span parstate) → (mv erp exprs span new-parstate)
This is called by parse-argument-expressions, after parsing the first argument expression, which we pass to this function as a singleton list. Here we read any additional arguments, each of which starts with a comma; we extend the list of arguments in the course of the recursion. We stop when the next token is not a comma.
We could extend the list in reverse (via cons), and then reverse it in the caller, but it probably does not make a big difference in performance.