.Net: Promote Liquid prompt template support to preview (#9665)

### Motivation and Context

- Promoting Liquid template support to preview
- Remove SKEXP0001 from allow_dangerously_set_content

### Description

<!-- Describe your changes, the overall approach, the underlying design.
These notes will help understanding how your code works. Thanks! -->

### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [ ] The code builds clean without any errors or warnings
- [ ] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [ ] All unit tests pass, and I have added new tests where possible
- [ ] I didn't break anyone 😄

dotnet/src/Extensions/PromptTemplates.Handlebars/HandlebarsPromptTemplateFactory.cs

@@ -15,7 +15,6 @@ public sealed class HandlebarsPromptTemplateFactory : IPromptTemplateFactory
     /// <summary>
     /// Default options for built-in Handlebars helpers.
     /// </summary>
-    /// TODO [@teresaqhoang]: Support override of default options
     private readonly HandlebarsPromptTemplateOptions _options;
 
     /// <summary>
@@ -32,7 +31,6 @@ public sealed class HandlebarsPromptTemplateFactory : IPromptTemplateFactory
     /// For prompts which are being used with a chat completion service this should be set to false to protect against prompt injection attacks.
     /// When using other AI services e.g. Text-To-Image this can be set to true to allow for more complex prompts.
     /// </remarks>
-    [Experimental("SKEXP0001")]
     public bool AllowDangerouslySetContent { get; init; } = false;
 
     /// <summary>

dotnet/src/Extensions/PromptTemplates.Liquid/LiquidPromptTemplate.cs

@@ -139,6 +139,7 @@ public async Task<string> RenderAsync(Kernel kernel, KernelArguments? arguments
         return renderedResult;
     }
 
+    #region Private
     private string Encoding(string text)
     {
         text = this.ReplaceReservedStringBackToColonIfNeeded(text);
@@ -286,4 +287,5 @@ protected override Expression VisitMemberExpression(MemberExpression memberExpre
             return memberExpression;
         }
     }
+    #endregion
 }

dotnet/src/Extensions/PromptTemplates.Liquid/PromptTemplates.Liquid.csproj

@@ -5,7 +5,8 @@
     <AssemblyName>Microsoft.SemanticKernel.PromptTemplates.Liquid</AssemblyName>
     <RootNamespace>$(AssemblyName)</RootNamespace>
     <TargetFrameworks>net8.0;netstandard2.0</TargetFrameworks>
-    <VersionSuffix>alpha</VersionSuffix>
+    <NoWarn>$(NoWarn);SKEXP0001</NoWarn>
+    <VersionSuffix>preview</VersionSuffix>
   </PropertyGroup>
 
   <Import Project="$(RepoRoot)/dotnet/nuget/nuget-package.props" />

dotnet/src/IntegrationTests/Connectors/Onnx/BertOnnxTextEmbeddingGenerationServiceTests.cs

@@ -9,9 +9,7 @@
 using System.Security.Cryptography;
 using System.Text;
 using System.Threading.Tasks;
-using Microsoft.Extensions.DependencyInjection;
 using Microsoft.SemanticKernel;
-using Microsoft.SemanticKernel.ChatCompletion;
 using Microsoft.SemanticKernel.Connectors.Onnx;
 using Microsoft.SemanticKernel.Embeddings;
 using Xunit;

dotnet/src/SemanticKernel.Abstractions/PromptTemplate/InputVariable.cs

@@ -99,7 +99,6 @@ public string Description
     /// For prompts which are being used with a chat completion service this should be set to false to protect against prompt injection attacks.
     /// When using other AI services e.g. Text-To-Image this can be set to true to allow for more complex prompts.
     /// </remarks>
-    [Experimental("SKEXP0001")]
     [JsonPropertyName("allow_dangerously_set_content")]
     public bool AllowDangerouslySetContent { get; set; } = false;
 }

dotnet/src/SemanticKernel.Abstractions/PromptTemplate/PromptTemplateConfig.cs

@@ -190,7 +190,6 @@ public Dictionary<string, PromptExecutionSettings> ExecutionSettings
     /// For prompts which are being used with a chat completion service this should be set to false to protect against prompt injection attacks.
     /// When using other AI services e.g. Text-To-Image this can be set to true to allow for more complex prompts.
     /// </remarks>
-    [Experimental("SKEXP0001")]
     [JsonPropertyName("allow_dangerously_set_content")]
     public bool AllowDangerouslySetContent { get; set; } = false;
 

dotnet/src/SemanticKernel.Core/PromptTemplate/KernelPromptTemplateFactory.cs

@@ -25,7 +25,6 @@ public sealed class KernelPromptTemplateFactory : IPromptTemplateFactory
     /// For prompts which are being used with a chat completion service this should be set to false to protect against prompt injection attacks.
     /// When using other AI services e.g. Text-To-Image this can be set to true to allow for more complex prompts.
     /// </remarks>
-    [Experimental("SKEXP0001")]
     public bool AllowDangerouslySetContent { get; init; } = false;
 
     /// <summary>