Rollup merge of #82128 - anall:feature/add_diagnostic_items, r=davidtwco

add diagnostic items for OsString/PathBuf/Owned as well as to_vec on slice

This is adding diagnostic items to be used by rust-lang/rust-clippy#6730, but my understanding is the clippy-side change does need to be done over there since I am adding a new clippy feature.

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

@@ -31,6 +31,7 @@ where
 /// implementing the `Clone` trait. But `Clone` works only for going from `&T`
 /// to `T`. The `ToOwned` trait generalizes `Clone` to construct owned data
 /// from any borrow of a given type.
+#[cfg_attr(not(test), rustc_diagnostic_item = "ToOwned")]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait ToOwned {
     /// The resulting type after obtaining ownership.

library/alloc/src/slice.rs

@@ -222,6 +222,7 @@ mod hack {
 }
 
 #[lang = "slice_alloc"]
+#[cfg_attr(not(test), rustc_diagnostic_item = "slice")]
 #[cfg(not(test))]
 impl<T> [T] {
     /// Sorts the slice.

library/alloc/src/string.rs

@@ -2175,6 +2175,7 @@ impl FromStr for String {
 /// implementation for free.
 ///
 /// [`Display`]: fmt::Display
+#[cfg_attr(not(test), rustc_diagnostic_item = "ToString")]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait ToString {
     /// Converts the given value to a `String`.