Merge PriorityQueue.Enumerator.MoveNextRare into MoveNext and use ThrowHelper for version checks (#118467)

* Merge PriorityQueue.Enumerator.MoveNextRare into MoveNext method

Co-authored-by: stephentoub <[email protected]>

* Use ThrowHelper.ThrowVersionCheckFailed() instead of manual exception throwing

Co-authored-by: stephentoub <[email protected]>

* Set _index to -1 in PriorityQueue enumerator to match List<T> pattern

Co-authored-by: stephentoub <[email protected]>

* Apply suggestions from code review

Co-authored-by: xtqqczze <[email protected]>

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: Stephen Toub <[email protected]>
Co-authored-by: xtqqczze <[email protected]>

Author: 3 people

src/libraries/System.Collections/src/System/Collections/Generic/PriorityQueue.cs

@@ -1012,25 +1012,20 @@ public bool MoveNext()
                 {
                     PriorityQueue<TElement, TPriority> localQueue = _queue;
 
-                    if (_version == localQueue._version && ((uint)_index < (uint)localQueue._size))
+                    if (_version != localQueue._version)
                     {
-                        _current = localQueue._nodes[_index];
-                        _index++;
-                        return true;
+                        ThrowHelper.ThrowVersionCheckFailed();
                     }
 
-                    return MoveNextRare();
-                }
-
-                private bool MoveNextRare()
-                {
-                    if (_version != _queue._version)
+                    if ((uint)_index < (uint)localQueue._size)
                     {
-                        throw new InvalidOperationException(SR.InvalidOperation_EnumFailedVersion);
+                        _current = localQueue._nodes[_index];
+                        _index++;
+                        return true;
                     }
 
-                    _index = _queue._size + 1;
                     _current = default;
+                    _index = -1;
                     return false;
                 }
 
@@ -1044,7 +1039,7 @@ void IEnumerator.Reset()
                 {
                     if (_version != _queue._version)
                     {
-                        throw new InvalidOperationException(SR.InvalidOperation_EnumFailedVersion);
+                        ThrowHelper.ThrowVersionCheckFailed();
                     }
 
                     _index = 0;