Add PriorityQueue to System.Collections.Generic (#43957)

src/libraries/System.Collections/ref/System.Collections.cs

@@ -378,6 +378,51 @@ public void Dispose() { }
             void System.Collections.IEnumerator.Reset() { }
         }
     }
+
+    public partial class PriorityQueue<TElement, TPriority>
+    {
+        public PriorityQueue() { }
+        public PriorityQueue(System.Collections.Generic.IComparer<TPriority>? comparer) { }
+        public PriorityQueue(System.Collections.Generic.IEnumerable<(TElement element, TPriority priority)> items) { }
+        public PriorityQueue(System.Collections.Generic.IEnumerable<(TElement element, TPriority priority)> items, System.Collections.Generic.IComparer<TPriority>? comparer) { }
+        public PriorityQueue(int initialCapacity) { }
+        public PriorityQueue(int initialCapacity, System.Collections.Generic.IComparer<TPriority>? comparer) { }
+        public System.Collections.Generic.IComparer<TPriority> Comparer { get { throw null; } }
+        public int Count { get { throw null; } }
+        public System.Collections.Generic.PriorityQueue<TElement, TPriority>.UnorderedItemsCollection UnorderedItems { get { throw null; } }
+        public void Clear() { }
+        public TElement Dequeue() { throw null; }
+        public void Enqueue(TElement element, TPriority priority) { }
+        public TElement EnqueueDequeue(TElement element, TPriority priority) { throw null; }
+        public void EnqueueRange(System.Collections.Generic.IEnumerable<(TElement element, TPriority priority)> items) { }
+        public void EnqueueRange(System.Collections.Generic.IEnumerable<TElement> elements, TPriority priority) { }
+        public int EnsureCapacity(int capacity) { throw null; }
+        public TElement Peek() { throw null; }
+        public void TrimExcess() { }
+        public bool TryDequeue([System.Diagnostics.CodeAnalysis.MaybeNullWhenAttribute(false)] out TElement element, [System.Diagnostics.CodeAnalysis.MaybeNullWhenAttribute(false)] out TPriority priority) { throw null; }
+        public bool TryPeek([System.Diagnostics.CodeAnalysis.MaybeNullWhenAttribute(false)] out TElement element, [System.Diagnostics.CodeAnalysis.MaybeNullWhenAttribute(false)] out TPriority priority) { throw null; }
+        public sealed partial class UnorderedItemsCollection : System.Collections.Generic.IEnumerable<(TElement element, TPriority priority)>, System.Collections.Generic.IReadOnlyCollection<(TElement element, TPriority priority)>, System.Collections.ICollection, System.Collections.IEnumerable
+        {
+            internal UnorderedItemsCollection(PriorityQueue<TElement, TPriority> queue) { }
+            public int Count { get { throw null; } }
+            bool System.Collections.ICollection.IsSynchronized { get { throw null; } }
+            object System.Collections.ICollection.SyncRoot { get { throw null; } }
+            void ICollection.CopyTo(System.Array array, int index) { }
+            public System.Collections.Generic.PriorityQueue<TElement, TPriority>.UnorderedItemsCollection.Enumerator GetEnumerator() { throw null; }
+            System.Collections.Generic.IEnumerator<(TElement element, TPriority priority)> System.Collections.Generic.IEnumerable<(TElement element, TPriority priority)>.GetEnumerator() { throw null; }
+            System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { throw null; }
+            public partial struct Enumerator : System.Collections.Generic.IEnumerator<(TElement element, TPriority priority)>, System.Collections.IEnumerator, System.IDisposable
+            {
+                (TElement element, TPriority priority) IEnumerator<(TElement element, TPriority priority)>.Current { get { throw null; } }
+                public void Dispose() { }
+                public bool MoveNext() { throw null; }
+                public (TElement element, TPriority priority) Current { get { throw null; } }
+                object System.Collections.IEnumerator.Current { get { throw null; } }
+                void System.Collections.IEnumerator.Reset() { }
+            }
+        }
+    }
+
     public partial class Queue<T> : System.Collections.Generic.IEnumerable<T>, System.Collections.Generic.IReadOnlyCollection<T>, System.Collections.ICollection, System.Collections.IEnumerable
     {
         public Queue() { }

src/libraries/System.Collections/src/System.Collections.csproj

@@ -13,6 +13,7 @@
     <Compile Include="$(CoreLibSharedDir)System\Collections\Generic\IDictionaryDebugView.cs"
              Link="Common\System\Collections\Generic\IDictionaryDebugView.cs" />
     <Compile Include="System\Collections\Generic\LinkedList.cs" />
+    <Compile Include="System\Collections\Generic\PriorityQueue.cs" />
     <Compile Include="System\Collections\Generic\Queue.cs" />
     <Compile Include="System\Collections\Generic\QueueDebugView.cs" />
     <Compile Include="System\Collections\Generic\SortedDictionary.cs" />