Using AllocateUninitializedArray in array pool (dotnet/coreclr#24504)

* Just use `new T[]` when elements are not pointer-free

* reduce zeroing out when not necessary.

* use AllocateUninitializedArray in ArrayPool

Signed-off-by: dotnet-bot <dotnet-bot@microsoft.com>

src/Common/src/CoreLib/System/Buffers/ConfigurableArrayPool.cs

@@ -100,13 +100,13 @@ public override T[] Rent(int minimumLength)
 
                 // The pool was exhausted for this buffer size.  Allocate a new buffer with a size corresponding
                 // to the appropriate bucket.
-                buffer = new T[_buckets[index]._bufferLength];
+                buffer = GC.AllocateUninitializedArray<T>(_buckets[index]._bufferLength);
             }
             else
             {
                 // The request was for a size too large for the pool.  Allocate an array of exactly the requested length.
                 // When it's returned to the pool, we'll simply throw it away.
-                buffer = new T[minimumLength];
+                buffer = GC.AllocateUninitializedArray<T>(minimumLength);
             }
 
             if (log.IsEnabled())
@@ -215,7 +215,7 @@ internal Bucket(int bufferLength, int numberOfBuffers, int poolId)
                 // for that slot, in which case we should do so now.
                 if (allocateBuffer)
                 {
-                    buffer = new T[_bufferLength];
+                    buffer = GC.AllocateUninitializedArray<T>(_bufferLength);
 
                     var log = ArrayPoolEventSource.Log;
                     if (log.IsEnabled())

src/Common/src/CoreLib/System/Buffers/TlsOverPerCoreLockedStacksArrayPool.cs

@@ -136,13 +136,13 @@ public override T[] Rent(int minimumLength)
                 }
 
                 // No buffer available.  Allocate a new buffer with a size corresponding to the appropriate bucket.
-                buffer = new T[_bucketArraySizes[bucketIndex]];
+                buffer = GC.AllocateUninitializedArray<T>(_bucketArraySizes[bucketIndex]);
             }
             else
             {
                 // The request was for a size too large for the pool.  Allocate an array of exactly the requested length.
                 // When it's returned to the pool, we'll simply throw it away.
-                buffer = new T[minimumLength];
+                buffer = GC.AllocateUninitializedArray<T>(minimumLength);
             }
 
             if (log.IsEnabled())