Fix operator precedence consistency in ASCIIUtility.GetIndexOfFirstNo…

…nAsciiByte (dotnet#64814)

The `&&` operator takes precedence over `||`, make it explicit by wrapping in parenthesis which also makes it consistent with other usages like https://github.com/dotnet/runtime/blob/57bfe474518ab5b7cfe6bf7424a79ce3af9d6657/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8Utility.Transcoding.cs#L887

Sse2 implies little endian so the check only needs to apply to AdvSimd.

src/libraries/System.Private.CoreLib/src/System/Text/ASCIIUtility.cs

@@ -89,7 +89,7 @@ public static unsafe nuint GetIndexOfFirstNonAsciiByte(byte* pBuffer, nuint buff
             // pmovmskb which we know are optimized, and (b) we can avoid downclocking the processor while
             // this method is running.
 
-            return (Sse2.IsSupported || AdvSimd.Arm64.IsSupported && BitConverter.IsLittleEndian)
+            return (Sse2.IsSupported || (AdvSimd.Arm64.IsSupported && BitConverter.IsLittleEndian))
                 ? GetIndexOfFirstNonAsciiByte_Intrinsified(pBuffer, bufferLength)
                 : GetIndexOfFirstNonAsciiByte_Default(pBuffer, bufferLength);
         }
@@ -1614,7 +1614,7 @@ public static unsafe nuint WidenAsciiToUtf16(byte* pAsciiBuffer, char* pUtf16Buf
             // pmovmskb which we know are optimized, and (b) we can avoid downclocking the processor while
             // this method is running.
 
-            if (BitConverter.IsLittleEndian && (Sse2.IsSupported || AdvSimd.Arm64.IsSupported))
+            if (Sse2.IsSupported || (AdvSimd.Arm64.IsSupported && BitConverter.IsLittleEndian))
             {
                 if (elementCount >= 2 * (uint)Unsafe.SizeOf<Vector128<byte>>())
                 {