internal: Standardize how we take iterator parameters in SyntaxFactory

[Giga-Bowser]

In my PR for migrating wrap/unwrap return type, I remarked about two different ways of taking many elements as a parameter, and it seemed like a matter of style at the time, but it turns out it actually matters a lot! Because if you provide a parameter taking IntoIterator + Clone using something a .map(), in which you construct additional elements using the same SyntaxFactory you're providing the parameter to, then by the lazy nature of iterators, there will be a looming mutable borrow on the RefCell for mappings, and the code will panic. So we need to be collecting the iterator to force any internal references be dropped.