Auto merge of #91359 - dtolnay:args, r=Mark-Simulacrum

Emit simpler code from format_args

I made this PR so that `cargo expand` dumps a less overwhelming amount of formatting-related code.

<br>

`println!("rust")` **Before:**

```rust
{
    ::std::io::_print(::core::fmt::Arguments::new_v1(&["rust\n"],
                                                     &match () {
                                                          _args => [],
                                                      }));
};
```

**After:**

```rust
{ ::std::io::_print(::core::fmt::Arguments::new_v1(&["rust\n"], &[])); };
```

`println!("{}", x)` **Before:**

```rust
{
    ::std::io::_print(::core::fmt::Arguments::new_v1(
        &["", "\n"],
        &match (&x,) {
            _args => [::core::fmt::ArgumentV1::new(
                _args.0,
                ::core::fmt::Display::fmt,
            )],
        },
    ));
};
```

**After:**

```rust
{
    ::std::io::_print(::core::fmt::Arguments::new_v1(
        &["", "\n"],
        &[::core::fmt::ArgumentV1::new(&x, ::core::fmt::Display::fmt)],
    ));
};
```

compiler/rustc_ast/src/ast.rs

@@ -39,6 +39,7 @@ use rustc_span::{Span, DUMMY_SP};
 use std::cmp::Ordering;
 use std::convert::TryFrom;
 use std::fmt;
+use std::mem;
 
 #[cfg(test)]
 mod tests;
@@ -1276,6 +1277,19 @@ impl Expr {
             ExprKind::Err => ExprPrecedence::Err,
         }
     }
+
+    pub fn take(&mut self) -> Self {
+        mem::replace(
+            self,
+            Expr {
+                id: DUMMY_NODE_ID,
+                kind: ExprKind::Err,
+                span: DUMMY_SP,
+                attrs: ThinVec::new(),
+                tokens: None,
+            },
+        )
+    }
 }
 
 /// Limit types of a range (inclusive or exclusive)