Improved loading of factors using permutation

Assembly for loading in the loop went from:
```asm
vmovss xmm2, [rax]
vbroadcastss xmm2, xmm2
vmovss xmm3, [rax+4]
vbroadcastss xmm3, xmm3
vinsertf128 ymm2, ymm2, xmm3, 1
```
To:
```asm
vmovsd xmm3, [rax]
vbroadcastsd ymm3, xmm3
vpermps ymm3, ymm1, ymm3
```

src/ImageSharp/Processing/Processors/Transforms/Resize/ResizeKernel.cs

@@ -76,11 +76,12 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
                 float* bufferStart = this.bufferPtr;
                 float* bufferEnd = bufferStart + (this.Length & ~1);
                 Vector256<float> result256 = Vector256<float>.Zero;
+                var mask = Vector256.Create(0, 0, 0, 0, 1, 1, 1, 1);
 
                 while (bufferStart < bufferEnd)
                 {
                     Vector256<float> rowItem256 = Unsafe.As<Vector4, Vector256<float>>(ref rowStartRef);
-                    var bufferItem256 = Vector256.Create(Vector128.Create(bufferStart[0]), Vector128.Create(bufferStart[1]));
+                    Vector256<float> bufferItem256 = Avx2.PermuteVar8x32(Vector256.Create(*(double*)bufferStart).AsSingle(), mask);
 
                     result256 = Fma.MultiplyAdd(rowItem256, bufferItem256, result256);