Revert string changes

Author: nathan-moore

src/libraries/System.Private.CoreLib/src/System/String.cs

@@ -487,9 +487,13 @@ public char[] ToCharArray(int startIndex, int length)
         [NonVersionable]
         public static bool IsNullOrEmpty([NotNullWhen(false)] string? value)
         {
+            // Using 0u >= (uint)value.Length rather than
+            // value.Length == 0 as it will elide the bounds check to
+            // the first char: value[0] if that is performed following the test
+            // for the same test cost.
             // Ternary operator returning true/false prevents redundant asm generation:
             // https://github.com/dotnet/runtime/issues/4207
-            return (value == null || 0 == value.Length) ? true : false;
+            return (value == null || 0u >= (uint)value.Length) ? true : false;
         }
 
         public static bool IsNullOrWhiteSpace([NotNullWhen(false)] string? value)
@@ -607,7 +611,6 @@ public StringRuneEnumerator EnumerateRunes()
         internal static unsafe int wcslen(char* ptr)
         {
             // IndexOf processes memory in aligned chunks, and thus it won't crash even if it accesses memory beyond the null terminator.
-            // This IndexOf behavior is an implementation detail of the runtime and callers outside System.Private.CoreLib must not depend on it.
             int length = SpanHelpers.IndexOf(ref *ptr, '\0', int.MaxValue);
             if (length < 0)
             {
@@ -621,7 +624,6 @@ internal static unsafe int wcslen(char* ptr)
         internal static unsafe int strlen(byte* ptr)
         {
             // IndexOf processes memory in aligned chunks, and thus it won't crash even if it accesses memory beyond the null terminator.
-            // This IndexOf behavior is an implementation detail of the runtime and callers outside System.Private.CoreLib must not depend on it.
             int length = SpanHelpers.IndexOf(ref *ptr, (byte)'\0', int.MaxValue);
             if (length < 0)
             {