Parse closure binders

This is first step in implementing RFC 3216.
- Parse `for<'a>` before closures in ast
  - Error in lowering
- Add `closure_lifetime_binder` feature

compiler/rustc_span/src/symbol.rs

@@ -459,6 +459,7 @@ symbols! {
         clone_closures,
         clone_from,
         closure,
+        closure_lifetime_binder,
         closure_to_fn_coercion,
         closure_track_caller,
         cmp,