[wasm] Try out a PackedSimd WideningLoader (#114811)

* Try out a PackedSimd WideningLoader

Author: lewing

src/libraries/System.Private.CoreLib/src/System/Text/Ascii.Equality.cs

@@ -7,6 +7,7 @@
 using System.Runtime.InteropServices;
 using System.Runtime.Intrinsics;
 using System.Runtime.Intrinsics.Arm;
+using System.Runtime.Intrinsics.Wasm;
 using System.Runtime.Intrinsics.X86;
 
 namespace System.Text
@@ -522,6 +523,11 @@ public static Vector128<ushort> Load128(ref byte ptr)
                     Vector128<byte> vec = Vector128.CreateScalarUnsafe(Unsafe.ReadUnaligned<long>(ref ptr)).AsByte();
                     return Sse2.UnpackLow(vec, Vector128<byte>.Zero).AsUInt16();
                 }
+                else if (PackedSimd.IsSupported)
+                {
+                    Vector128<byte> vec = Vector128.CreateScalarUnsafe(Unsafe.ReadUnaligned<long>(ref ptr)).AsByte();
+                    return PackedSimd.ZeroExtendWideningLower(vec);
+                }
                 else
                 {
                     (Vector64<ushort> lower, Vector64<ushort> upper) = Vector64.Widen(Vector64.LoadUnsafe(ref ptr));