Fix prepared script performance regression from shared identifier cache thrashing

Jint.Benchmark/Jint.Benchmark.csproj

@@ -21,6 +21,7 @@
   </PropertyGroup>
   <ItemGroup>
     <None Include=".\Scripts\*.*" CopyToOutputDirectory="PreserveNewest" />
+    <None Include=".\Scripts\template-rendering\**\*.*" CopyToOutputDirectory="PreserveNewest" LinkBase="Scripts\template-rendering" />
     <None Include="..\Jint.Tests.CommonScripts\Scripts\**" CopyToOutputDirectory="PreserveNewest" LinkBase="Scripts" />
   </ItemGroup>
   <ItemGroup>

Jint.Benchmark/PreparedScriptBenchmark.cs

@@ -0,0 +1,71 @@
+using BenchmarkDotNet.Attributes;
+
+namespace Jint.Benchmark;
+
+/// <summary>
+/// Replicates the exact pattern from JavaScriptEngineSwitcher's JsExecutionHeavyBenchmark:
+/// a Handlebars template rendering library is loaded on 4 separate engine instances,
+/// each calling renderTemplate() with different content items.
+/// See: https://github.com/Taritsyn/JavaScriptEngineSwitcher/blob/master/test/JavaScriptEngineSwitcher.Benchmarks/JsExecutionHeavyBenchmark.cs
+/// </summary>
+[MemoryDiagnoser]
+public class PreparedScriptBenchmark
+{
+    private string _libraryCode = null!;
+    private Prepared<Script> _preparedLibrary;
+    private ContentItem[] _contentItems = null!;
+
+    [GlobalSetup]
+    public void Setup()
+    {
+        var handlebars = File.ReadAllText("Scripts/template-rendering/lib/handlebars.js");
+        var helpers = File.ReadAllText("Scripts/template-rendering/lib/helpers.js");
+        _libraryCode = handlebars + "\n" + helpers;
+        _preparedLibrary = Engine.PrepareScript(_libraryCode);
+
+        var contentDir = "Scripts/template-rendering/content";
+        string[] names = ["hello-world", "contacts", "js-engines", "web-browser-family-tree"];
+        _contentItems = names.Select(name => new ContentItem(
+            File.ReadAllText(Path.Combine(contentDir, name, "template.handlebars")),
+            File.ReadAllText(Path.Combine(contentDir, name, "data.json"))
+        )).ToArray();
+    }
+
+    [Benchmark(Baseline = true)]
+    public void ExecuteStringOnMultipleEngines()
+    {
+        RenderTemplates(withPrecompilation: false);
+    }
+
+    [Benchmark]
+    public void ExecutePreparedOnMultipleEngines()
+    {
+        RenderTemplates(withPrecompilation: true);
+    }
+
+    private void RenderTemplates(bool withPrecompilation)
+    {
+        // First engine: load library and render first item
+        var engine = new Engine();
+        if (withPrecompilation)
+            engine.Execute(_preparedLibrary);
+        else
+            engine.Execute(_libraryCode);
+
+        engine.Invoke("renderTemplate", _contentItems[0].Template, _contentItems[0].Data);
+
+        // Remaining engines: each loads the same library and renders one item
+        for (int i = 1; i < _contentItems.Length; i++)
+        {
+            engine = new Engine();
+            if (withPrecompilation)
+                engine.Execute(_preparedLibrary);
+            else
+                engine.Execute(_libraryCode);
+
+            engine.Invoke("renderTemplate", _contentItems[i].Template, _contentItems[i].Data);
+        }
+    }
+
+    private sealed record ContentItem(string Template, string Data);
+}

Jint.Benchmark/Scripts/template-rendering/content/contacts/data.json

@@ -0,0 +1,20 @@
+{
+  "lastName": "Пупкин",
+  "firstName": "Василий",
+  "patronymic": "Иванович",
+  "address": {
+    "postalCode": 392032,
+    "country": "Россия",
+    "state": "Тамбовская область",
+    "city": "Тамбов",
+    "street": "Магистральная",
+    "houseNumber": "41к7",
+    "floor": 8,
+    "apartmentNumber": 115
+  },
+  "homePhone": "+7 (4752) 555-55-55",
+  "mobilePhone": "+7 (999) 689-99-99",
+  "email": "pupkin@mail.ru",
+  "website": "http:\/\/pupkin.narod.ru",
+  "icq": 698426795
+}

Jint.Benchmark/Scripts/template-rendering/content/contacts/template.handlebars

@@ -0,0 +1,13 @@
+<address>
+	<strong><abbr title="Фамилия Имя Отчество">Ф.И.О.</abbr>:</strong> {{lastName}} {{firstName}} {{patronymic}}<br />
+	<strong>Адрес:</strong>
+	{{#with address}}
+		{{postalCode}}, {{country}}, {{state}}, {{city}}, ул. {{street}}, д. {{houseNumber}}, кв. {{apartmentNumber}}
+	{{/with}}
+	<br />
+	<strong>Дом. тел.:</strong> {{homePhone}}<br />
+	<strong>Моб. тел.:</strong> {{mobilePhone}}<br />
+	<strong>Email:</strong> <a href="mailto:{{email}}">{{email}}</a><br />
+	<strong>Сайт:</strong> {{{link website website false}}}<br />
+	<strong>ICQ:</strong> <img src="http://status.icq.com/online.gif?icq={{icq}}&img=26" alt="ICQ статус" />{{icq}}
+</address>

Jint.Benchmark/Scripts/template-rendering/content/hello-world/data.json

@@ -0,0 +1,6 @@
+{
+  "lastName": "Pupkin",
+  "firstName": "Vasilii",
+  "patronymic": "Ivanovich",
+  "occupation": "Enikeyschik"
+}

Jint.Benchmark/Scripts/template-rendering/content/hello-world/template.handlebars

@@ -0,0 +1,4 @@
+<div class="greeting">
+	{{!-- Welcome by first name and patronymic --}}
+	Hello, {{firstName}} {{patronymic}}!
+</div>