Rollup merge of #134834 - dtolnay:unnamedcall, r=compiler-errors

Skip parenthesis around tuple struct field calls

The pretty-printer previously did not distinguish between named vs unnamed fields when printing a function call containing a struct field. It would print the call as `(self.fun)()` for a named field which is correct, and `(self.0)()` for an unnamed field which is redundant.

This PR changes function calls of tuple struct fields to print without parens.

**Before:**

```rust
struct Tuple(fn());

fn main() {
    let tuple = Tuple(|| {});
    (tuple.0)();
}
```

**After:**

```rust
struct Tuple(fn());

fn main() {
    let tuple = Tuple(|| {});
    tuple.0();
}
```

compiler/rustc_ast_pretty/src/pprust/state/expr.rs

@@ -213,7 +213,9 @@ impl<'a> State<'a> {
 
     fn print_expr_call(&mut self, func: &ast::Expr, args: &[P<ast::Expr>], fixup: FixupContext) {
         let needs_paren = match func.kind {
-            ast::ExprKind::Field(..) => true,
+            // In order to call a named field, needs parens: `(self.fun)()`
+            // But not for an unnamed field: `self.0()`
+            ast::ExprKind::Field(_, name) => !name.is_numeric(),
             _ => func.precedence() < ExprPrecedence::Unambiguous,
         };