Move TrailingZeroCountFallback to common SpanHelpers

So it can be used by other types than byte

Author: benaadams

src/System.Private.CoreLib/shared/System/SpanHelpers.Byte.cs

@@ -1244,18 +1244,5 @@ private static int LocateLastFoundByte(ulong match)
                                                        0x03ul << 32 |
                                                        0x02ul << 40 |
                                                        0x01ul << 48) + 1;
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static int TrailingZeroCountFallback(int matches)
-        {
-            // https://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightMultLookup
-            return TrailingCountMultiplyDeBruijn[(int)(((uint)((matches & -matches) * 0x077CB531U)) >> 27)];
-        }
-
-        private static ReadOnlySpan<byte> TrailingCountMultiplyDeBruijn => new byte[32]
-        {
-            0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
-            31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9
-        };
     }
 }

src/System.Private.CoreLib/shared/System/SpanHelpers.cs

@@ -5,7 +5,7 @@
 using System.Diagnostics;
 using System.Globalization;
 using System.Runtime;
-
+using System.Runtime.CompilerServices;
 using Internal.Runtime.CompilerServices;
 
 #if BIT64
@@ -411,5 +411,18 @@ public static unsafe void ClearWithReferences(ref IntPtr ip, nuint pointerSizeLe
             // Write only element.
             ip = default;
         }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static int TrailingZeroCountFallback(int matches)
+        {
+            // https://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightMultLookup
+            return TrailingCountMultiplyDeBruijn[(int)(((uint)((matches & -matches) * 0x077CB531U)) >> 27)];
+        }
+
+        private static ReadOnlySpan<byte> TrailingCountMultiplyDeBruijn => new byte[32]
+        {
+            0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
+            31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9
+        };
     }
 }