Auto merge of #99099 - Stargateur:phantomdata_debug, r=joshtriplett

Add T to PhantomData impl Debug

This add debug information for `PhantomData`, I believe it's make sense to add this to debug impl of `PhantomData` since `T` is what define what is the `PhantomData` just write `"PhantomData"` is not very useful for debugging.

Alternative:

* `PhantomData::<{}>`
* `PhantomData { t: "str_type" }`

`@rustbot` label +T-libs-api -T-libs

Author: bors

Diff for: library/core/src/fmt/mod.rs

@@ -2610,7 +2610,7 @@ impl Debug for () {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized> Debug for PhantomData<T> {
     fn fmt(&self, f: &mut Formatter<'_>) -> Result {
-        f.debug_struct("PhantomData").finish()
+        write!(f, "PhantomData<{}>", crate::any::type_name::<T>())
     }
 }