add diagnostic items

Add diagnostic items to the following types:
  OsString (os_string_type)
  PathBuf (path_buf_type)
  Owned (to_owned_trait)

As well as the to_vec method on slice/[T]

library/alloc/src/borrow.rs

@@ -32,6 +32,7 @@ where
 /// to `T`. The `ToOwned` trait generalizes `Clone` to construct owned data
 /// from any borrow of a given type.
 #[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "to_owned_trait")]
 pub trait ToOwned {
     /// The resulting type after obtaining ownership.
     #[stable(feature = "rust1", since = "1.0.0")]

library/alloc/src/slice.rs

@@ -442,6 +442,7 @@ impl<T> [T] {
     /// // Here, `s` and `x` can be modified independently.
     /// ```
     #[rustc_conversion_suggestion]
+    #[rustc_diagnostic_item = "slice_to_vec_method"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn to_vec(&self) -> Vec<T>