More diagnostic items for Clippy usage

This adds a couple of more diagnostic items to be used in Clippy.
I chose these particular ones because they were the types which we seem
to check for the most in Clippy. I'm not sure if the
`cfg_attr(not(test))` is needed, but it was also used for `Vec` and a
few other types.

src/liballoc/collections/vec_deque.rs

@@ -50,6 +50,7 @@ const MAXIMUM_ZST_CAPACITY: usize = 1 << (64 - 1); // Largest possible power of
 /// [`pop_front`]: #method.pop_front
 /// [`extend`]: #method.extend
 /// [`append`]: #method.append
+#[cfg_attr(not(test), rustc_diagnostic_item = "vecdeque_type")]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct VecDeque<T> {
     // tail and head are pointers into the buffer. Tail always points

src/liballoc/string.rs

@@ -278,6 +278,7 @@ use crate::vec::Vec;
 /// [`Deref`]: ../../std/ops/trait.Deref.html
 /// [`as_str()`]: struct.String.html#method.as_str
 #[derive(PartialOrd, Eq, Ord)]
+#[cfg_attr(not(test), rustc_diagnostic_item = "string_type")]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct String {
     vec: Vec<u8>,

src/libstd/collections/hash/map.rs

@@ -198,6 +198,7 @@ use crate::sys;
 /// ```
 
 #[derive(Clone)]
+#[cfg_attr(not(test), rustc_diagnostic_item = "hashmap_type")]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct HashMap<K, V, S = RandomState> {
     base: base::HashMap<K, V, S>,

src/libstd/collections/hash/set.rs

@@ -105,6 +105,7 @@ use super::map::{self, HashMap, Keys, RandomState};
 /// [`PartialEq`]: ../../std/cmp/trait.PartialEq.html
 /// [`RefCell`]: ../../std/cell/struct.RefCell.html
 #[derive(Clone)]
+#[cfg_attr(not(test), rustc_diagnostic_item = "hashset_type")]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct HashSet<T, S = RandomState> {
     map: HashMap<T, (), S>,

src/libstd/sync/mutex.rs

@@ -108,6 +108,7 @@ use crate::sys_common::poison::{self, LockResult, TryLockError, TryLockResult};
 /// *guard += 1;
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "mutex_type")]
 pub struct Mutex<T: ?Sized> {
     // Note that this mutex is in a *box*, not inlined into the struct itself.
     // Once a native mutex has been used once, its address can never change (it