SpanHelpers IndexOfAny-methods use sentinel-value (#25970)

* SpanHelpers IndexOfAny-methods use sentinel-value

Instead of having _valueLength_-times an if-check in the loop,
a sentinel value is used and hence only one final checks needs to done.

Perf-win depends on the size of _valueLength_, the greater the more win.

* LastIndexOf initializes index with -1 instead of int.MinValue

As of PR-feedback.

* Better checks based on if instead of ternary operator

As of PR-feedback.

* SpanHelpers.byte.cs IndexOfAny can avoid int.MaxValue due to unit-trick

As of PR-Feedback

Author: gfoidl

src/System.Memory/src/System/SpanHelpers.T.cs

@@ -63,10 +63,7 @@ public static int LastIndexOfAny<T>(ref T searchSpace, int searchSpaceLength, re
             for (int i = 0; i < valueLength; i++)
             {
                 var tempIndex = LastIndexOf(ref searchSpace, Unsafe.Add(ref value, i), searchSpaceLength);
-                if (tempIndex != -1)
-                {
-                    index = (index == -1 || index < tempIndex) ? tempIndex : index;
-                }
+                if (tempIndex > index) index = tempIndex;
             }
             return index;
         }

src/System.Memory/src/System/SpanHelpers.byte.cs

@@ -64,10 +64,7 @@ public static int IndexOfAny(ref byte searchSpace, int searchSpaceLength, ref by
             for (int i = 0; i < valueLength; i++)
             {
                 var tempIndex = IndexOf(ref searchSpace, Unsafe.Add(ref value, i), searchSpaceLength);
-                if (tempIndex != -1)
-                {
-                    index = (index == -1 || index > tempIndex) ? tempIndex : index;
-                }
+                if ((uint)tempIndex < (uint)index) index = tempIndex;
             }
             return index;
         }
@@ -84,10 +81,7 @@ public static int LastIndexOfAny(ref byte searchSpace, int searchSpaceLength, re
             for (int i = 0; i < valueLength; i++)
             {
                 var tempIndex = LastIndexOf(ref searchSpace, Unsafe.Add(ref value, i), searchSpaceLength);
-                if (tempIndex != -1)
-                {
-                    index = (index == -1 || index < tempIndex) ? tempIndex : index;
-                }
+                if (tempIndex > index) index = tempIndex;
             }
             return index;
         }