Rollup merge of #103774 - compiler-errors:dyn-trait-in-type-name, r=eholk

Format `dyn Trait` better in `type_name` intrinsic

Noticed this in #103764 (though not related to that PR at all!)

```rust
trait Foo {
    type Bar;
}

fn main() {
    println!(
        "`dyn Fn(i32, i32) -> i32` => `{}`",
        std::any::type_name::<dyn Fn(i32, i32) -> i32>()
    );
    println!(
        "`dyn Foo<Bar = i32> + Send + Sync` => `{}`",
        std::any::type_name::<dyn Foo<Bar = i32> + Send + Sync>()
    );
}
```

```
`dyn Fn(i32, i32) -> i32` => `dyn core::ops::function::Fn<(i32, i32)>+Output = i32`
`dyn Foo<Bar = i32> + Send + Sync` => `dyn playground::Foo+Bar = i32+core::marker::Sync+core::marker::Send`
```

Just reuse `pretty_print_dyn_existential` which already makes an attempt to make its output stable.

Author: Dylan-DPC

core/tests/any.rs

@@ -131,6 +131,24 @@ fn distinct_type_names() {
     assert_ne!(type_name_of_val(Velocity), type_name_of_val(Velocity(0.0, -9.8)),);
 }
 
+#[cfg(not(bootstrap))]
+#[test]
+fn dyn_type_name() {
+    trait Foo {
+        type Bar;
+    }
+
+    assert_eq!(
+        "dyn core::ops::function::Fn(i32, i32) -> i32",
+        std::any::type_name::<dyn Fn(i32, i32) -> i32>()
+    );
+    assert_eq!(
+        "dyn coretests::any::dyn_type_name::Foo<Bar = i32> \
+        + core::marker::Send + core::marker::Sync",
+        std::any::type_name::<dyn Foo<Bar = i32> + Send + Sync>()
+    );
+}
+
 // Test the `Provider` API.
 
 struct SomeConcreteType {