Auto merge of #17941 - ChayimFriedman2:pre-closure-to-fn, r=Veykril

Preliminary work for #17940

I split the PR as requested, and made small commits.

crates/intern/src/symbol/symbols.rs

@@ -240,6 +240,7 @@ define_symbols! {
     fundamental,
     future_trait,
     future,
+    future_output,
     Future,
     ge,
     get_context,
@@ -274,6 +275,7 @@ define_symbols! {
     iter_mut,
     iter,
     Iterator,
+    iterator,
     keyword,
     lang,
     le,