Performance improvement for ReplaceFirst function (#13018)

* Some benchmarks for replacefirst & span method

(cherry picked from commit e550a4ce3a)

tests/Umbraco.Tests.Benchmarks/StringReplaceFirstBenchmarks.cs

@@ -0,0 +1,66 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Security.Cryptography;
+using System.Text;
+using System.Threading.Tasks;
+using BenchmarkDotNet.Attributes;
+using Umbraco.Tests.Benchmarks.Config;
+
+namespace Umbraco.Tests.Benchmarks;
+
+[QuickRunWithMemoryDiagnoserConfig]
+public class StringReplaceFirstBenchmarks
+{
+    [Params("Test string",
+        "This is a test string that contains multiple test entries",
+        "This is a string where the searched value is very far back. The system needs to go through all of this code before it reaches the test")]
+    public string Text { get; set; }
+    public string Search { get; set; }
+    public string Replace { get; set; }
+
+    [GlobalSetup]
+    public void Setup()
+    {
+        Search = "test";
+        Replace = "release";
+    }
+
+    [Benchmark(Baseline = true, Description = "Replace first w/ substring")]
+    public string SubstringReplaceFirst()
+    {
+        var pos = Text.IndexOf(Search, StringComparison.InvariantCulture);
+
+        if (pos < 0)
+        {
+            return Text;
+        }
+
+        return Text.Substring(0, pos) + Replace + Text.Substring(pos + Search.Length);
+    }
+
+    [Benchmark(Description = "Replace first w/ span")]
+    public string SpanReplaceFirst()
+    {
+        var spanText = Text.AsSpan();
+        var pos = spanText.IndexOf(Search, StringComparison.InvariantCulture);
+
+        if (pos < 0)
+        {
+            return Text;
+        }
+
+        return string.Concat(spanText[..pos], Replace.AsSpan(), spanText[(pos + Search.Length)..]);
+    }
+
+    //|                       Method |                 Text |      Mean |    Error |   StdDev | Ratio | RatioSD |  Gen 0 | Allocated |
+    //|----------------------------- |--------------------- |----------:|---------:|---------:|------:|--------:|-------:|----------:|
+    //| 'Replace first w/ substring' |          Test string |  46.08 ns | 25.83 ns | 1.416 ns |  1.00 |    0.00 |      - |         - |
+    //|      'Replace first w/ span' |          Test string |  38.59 ns | 19.46 ns | 1.067 ns |  0.84 |    0.05 |      - |         - |
+    //|                              |                      |           |          |          |       |         |        |           |
+    //| 'Replace first w/ substring' |  This(...)test[134] | 407.89 ns | 52.08 ns | 2.855 ns |  1.00 |    0.00 | 0.1833 |     584 B |
+    //|      'Replace first w/ span' |  This(...)test[134] | 372.99 ns | 58.38 ns | 3.200 ns |  0.91 |    0.01 | 0.0941 |     296 B |
+    //|                              |                      |           |          |          |       |         |        |           |
+    //| 'Replace first w/ substring' | This(...)tries[57] | 113.16 ns | 27.95 ns | 1.532 ns |  1.00 |    0.00 | 0.0961 |     304 B |
+    //|      'Replace first w/ span' | This(...)tries[57] |  76.57 ns | 17.86 ns | 0.979 ns |  0.68 |    0.01 | 0.0455 |     144 B |
+}