Shrink Nonterminal.

By heap allocating the argument within `NtPath`, `NtVis`, and `NtStmt`.
This slightly reduces cumulative and peak allocation amounts, most
notably on `deep-vector`.

compiler/rustc_parse/src/parser/stmt.rs

@@ -54,7 +54,7 @@ impl<'a> Parser<'a> {
             stmt.visit_attrs(|stmt_attrs| {
                 attrs.prepend_to_nt_inner(stmt_attrs);
             });
-            return Ok(Some(stmt));
+            return Ok(Some(stmt.into_inner()));
         }
 
         Ok(Some(if self.token.is_keyword(kw::Let) {
@@ -535,7 +535,7 @@ impl<'a> Parser<'a> {
         recover: AttemptLocalParseRecovery,
     ) -> PResult<'a, Option<Stmt>> {
         // Skip looking for a trailing semicolon when we have an interpolated statement.
-        maybe_whole!(self, NtStmt, |x| Some(x));
+        maybe_whole!(self, NtStmt, |x| Some(x.into_inner()));
 
         let Some(mut stmt) = self.parse_stmt_without_recovery(true, ForceCollect::No)? else {
             return Ok(None);