Removing unsafe parts of Decode method in QueryStringEnumerable (#56630)

* Using TryUnescapeDataString to avoid extra string allocation

---------

Co-authored-by: ladeak <ladeak87@windowslive.com>

src/Http/Http/perf/Microbenchmarks/QueryCollectionBenchmarks.cs

@@ -13,19 +13,10 @@ namespace Microsoft.AspNetCore.Http;
 [CategoriesColumn]
 public class QueryCollectionBenchmarks
 {
-    private string _queryString;
-    private string _singleValue;
-    private string _singleValueWithPlus;
-    private string _encoded;
-
-    [IterationSetup]
-    public void Setup()
-    {
-        _queryString = "?key1=value1&key2=value2&key3=value3&key4=&key5=";
-        _singleValue = "?key1=value1";
-        _singleValueWithPlus = "?key1=value1+value2+value3";
-        _encoded = "?key1=value%231";
-    }
+    private const string _queryString = "?key1=value1&key2=value2&key3=value3&key4=&key5=";
+    private const string _singleValue = "?key1=value1";
+    private const string _singleValueWithPlus = "?key1=value1+value2+value3";
+    private const string _encoded = "?key1=value%231";
 
     [Benchmark(Description = "ParseNew")]
     [BenchmarkCategory("QueryString")]

src/Shared/QueryStringEnumerable.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Buffers;
+using System.Diagnostics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Runtime.Intrinsics;
@@ -88,21 +89,18 @@ public ReadOnlyMemory<char> DecodeName()
         public ReadOnlyMemory<char> DecodeValue()
             => Decode(EncodedValue);
 
-        private static unsafe ReadOnlyMemory<char> Decode(ReadOnlyMemory<char> chars)
+        private static ReadOnlyMemory<char> Decode(ReadOnlyMemory<char> chars)
         {
-            // If the value is short, it's cheap to check up front if it really needs decoding. If it doesn't,
-            // then we can save some allocations.
-            if (chars.Length < 16 && chars.Span.IndexOfAny('%', '+') < 0)
+            ReadOnlySpan<char> source = chars.Span;
+            if (!source.ContainsAny('%', '+'))
             {
                 return chars;
             }
-
-#pragma warning disable CS8500 // This takes the address of, gets the size of, or declares a pointer to a managed type
-            ReadOnlySpan<char> span = chars.Span;
-            return Uri.UnescapeDataString(
-                string.Create(span.Length,
-                    (IntPtr)(&span), static (dest, ptr) => ((ReadOnlySpan<char>*)ptr)->Replace(dest, '+', ' '))).AsMemory();
-#pragma warning restore CS8500
+            var buffer = new char[source.Length];
+            source.Replace(buffer, '+', ' ');
+            var success = Uri.TryUnescapeDataString(buffer, buffer, out var unescapedLength);
+            Debug.Assert(success);
+            return buffer.AsMemory(0, unescapedLength);
         }
     }