Use Span version of Sort() to reduce allocations

src/ImageSharp/Formats/Webp/Lossless/HuffmanUtils.cs

@@ -202,9 +202,14 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
                 }
 
                 // Build the Huffman tree.
+#if NET5_0_OR_GREATER
+                Span<HuffmanTree> treeSlice = tree.AsSpan().Slice(0, treeSize);
+                treeSlice.Sort(HuffmanTree.Compare);
+#else
                 HuffmanTree[] treeCopy = tree.AsSpan().Slice(0, treeSize).ToArray();
                 Array.Sort(treeCopy, HuffmanTree.Compare);
                 treeCopy.AsSpan().CopyTo(tree);
+#endif
 
                 if (treeSize > 1)
                 {

src/ImageSharp/Formats/Webp/Lossless/Vp8LEncoder.cs

@@ -1204,9 +1204,14 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
                 return false;
             }
 
+#if NET5_0_OR_GREATER
+            var paletteSlice = palette.Slice(0, this.PaletteSize);
+            paletteSlice.Sort();
+#else
             uint[] paletteArray = palette.Slice(0, this.PaletteSize).ToArray();
             Array.Sort(paletteArray);
             paletteArray.CopyTo(palette);
+#endif
 
             if (PaletteHasNonMonotonousDeltas(palette, this.PaletteSize))
             {