Safe utf8 string conversion (#9131)

Author: benaadams

src/Servers/Kestrel/Core/src/Internal/Http/PathNormalizer.cs

@@ -35,7 +35,7 @@ public static string DecodePath(Span<byte> path, bool pathEncoded, string rawTar
                 // https://tools.ietf.org/html/rfc3986#section-2.2
                 pathLength = RemoveDotSegments(path.Slice(0, pathLength));
 
-                return GetUtf8String(path.Slice(0, pathLength));
+                return Encoding.UTF8.GetString(path.Slice(0, pathLength));
             }
 
             pathLength = RemoveDotSegments(path);
@@ -50,16 +50,6 @@ public static string DecodePath(Span<byte> path, bool pathEncoded, string rawTar
             return path.Slice(0, pathLength).GetAsciiStringNonNullCharacters();
         }
 
-        private static unsafe string GetUtf8String(Span<byte> path)
-        {
-            // .NET 451 doesn't have pointer overloads for Encoding.GetString so we
-            // copy to an array
-            fixed (byte* pointer = path)
-            {
-                return Encoding.UTF8.GetString(pointer, path.Length);
-            }
-        }
-
         // In-place implementation of the algorithm from https://tools.ietf.org/html/rfc3986#section-5.2.4
         public static unsafe int RemoveDotSegments(Span<byte> input)
         {