Auto merge of rust-lang#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)],
    ));
};
```

Author: bors

tests/ui/to_string_in_display.stderr

@@ -6,5 +6,14 @@ LL |         write!(f, "{}", self.to_string())
    |
    = note: `-D clippy::to-string-in-display` implied by `-D warnings`
 
-error: aborting due to previous error
+error: unnecessary use of `to_string`
+  --> $DIR/to_string_in_display.rs:55:50
+   |
+LL |             Self::E(string) => write!(f, "E {}", string.to_string()),
+   |                                                  ^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D clippy::unnecessary-to-owned` implied by `-D warnings`
+   = note: this error originates in the macro `$crate::format_args` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 2 previous errors