.Net: Promote OpenAPI package to preview (microsoft#9704)

### Motivation, Context and Description
Promote Functions.OpenApi package to preview. Closes:
microsoft#9636

Author: SergeyMenshykh

dotnet/src/Functions/Functions.OpenApi/AssemblyInfo.cs

@@ -2,6 +2,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Net.Http;
 using Microsoft.Extensions.Logging;
 using Microsoft.SemanticKernel.Http;
@@ -46,6 +47,7 @@ public class OpenApiFunctionExecutionParameters
     /// To support more complex payloads, it should be disabled and the payload should be provided via the 'payload' argument.
     /// See the 'Providing Payload for OpenAPI Functions' ADR for more details: https://github.com/microsoft/semantic-kernel/blob/main/docs/decisions/0062-open-api-payload.md
     /// </summary>
+    [Experimental("SKEXP0040")]
     public bool EnableDynamicPayload { get; set; }
 
     /// <summary>
@@ -56,11 +58,13 @@ public class OpenApiFunctionExecutionParameters
     /// the parameters 'sender.email' and 'sender.receiver' will be correctly resolved from arguments with the same names.
     /// See the 'Providing Payload for OpenAPI Functions' ADR for more details: https://github.com/microsoft/semantic-kernel/blob/main/docs/decisions/0062-open-api-payload.md
     /// </summary>
+    [Experimental("SKEXP0040")]
     public bool EnablePayloadNamespacing { get; set; }
 
     /// <summary>
     /// Optional list of HTTP operations to skip when importing the OpenAPI document.
     /// </summary>
+    [Experimental("SKEXP0040")]
     public IList<string> OperationsToExclude { get; set; }
 
     /// <summary>
@@ -72,6 +76,7 @@ public class OpenApiFunctionExecutionParameters
     /// as a stream rather than as a string.
     /// If the custom reader is not provided, or the reader returns null, the internal reader is used.
     /// </summary>
+    [Experimental("SKEXP0040")]
     public HttpResponseContentReader? HttpResponseContentReader { get; set; }
 
     /// <summary>
@@ -94,6 +99,7 @@ public class OpenApiFunctionExecutionParameters
     /// <param name="enablePayloadNamespacing">Determines whether payload parameter names are augmented with namespaces.
     /// Namespaces prevent naming conflicts by adding the parent parameter name as a prefix, separated by dots.</param>
     /// <param name="operationsToExclude">Optional list of operations not to import, e.g. in case they are not supported</param>
+    [Experimental("SKEXP0040")]
     public OpenApiFunctionExecutionParameters(
         HttpClient? httpClient = null,
         AuthenticateRequestAsyncCallback? authCallback = null,

dotnet/src/Functions/Functions.OpenApi/Extensions/OpenApiFunctionExecutionParameters.cs

@@ -4,7 +4,8 @@
     <AssemblyName>Microsoft.SemanticKernel.Plugins.OpenApi</AssemblyName>
     <RootNamespace>$(AssemblyName)</RootNamespace>
     <TargetFrameworks>net8.0;netstandard2.0</TargetFrameworks>
-    <VersionSuffix>alpha</VersionSuffix>
+    <NoWarn>$(NoWarn);SKEXP0040</NoWarn>
+    <VersionSuffix>preview</VersionSuffix>
   </PropertyGroup>
   <Import Project="$(RepoRoot)/dotnet/nuget/nuget-package.props" />
   <Import Project="$(RepoRoot)/dotnet/src/InternalUtilities/src/InternalUtilities.props" />

dotnet/src/Functions/Functions.OpenApi/Functions.OpenApi.csproj

@@ -1,5 +1,6 @@
 // Copyright (c) Microsoft. All rights reserved.
 
+using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -11,4 +12,5 @@ namespace Microsoft.SemanticKernel.Plugins.OpenApi;
 /// <param name="context">The context containing HTTP operation details.</param>
 /// <param name="cancellationToken">The cancellation token.</param>
 /// <returns>The HTTP response content.</returns>
+[Experimental("SKEXP0040")]
 public delegate Task<object?> HttpResponseContentReader(HttpResponseContentReaderContext context, CancellationToken cancellationToken = default);

dotnet/src/Functions/Functions.OpenApi/HttpResponseContentReader.cs

@@ -1,12 +1,14 @@
 // Copyright (c) Microsoft. All rights reserved.
 
+using System.Diagnostics.CodeAnalysis;
 using System.Net.Http;
 
 namespace Microsoft.SemanticKernel.Plugins.OpenApi;
 
 /// <summary>
 /// Represents the context for HTTP response content reader.
 /// </summary>
+[Experimental("SKEXP0040")]
 public sealed class HttpResponseContentReaderContext
 {
     /// <summary>

dotnet/src/Functions/Functions.OpenApi/HttpResponseContentReaderContext.cs

@@ -3,6 +3,7 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.IO;
 using System.Linq;
@@ -26,6 +27,7 @@ namespace Microsoft.SemanticKernel.Plugins.OpenApi;
 /// <summary>
 /// Parser for OpenAPI documents.
 /// </summary>
+[Experimental("SKEXP0040")]
 public sealed class OpenApiDocumentParser(ILoggerFactory? loggerFactory = null)
 {
     /// <summary>

dotnet/src/Functions/Functions.OpenApi/OpenApi/OpenApiDocumentParser.cs

@@ -1,12 +1,14 @@
 // Copyright (c) Microsoft. All rights reserved.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Microsoft.SemanticKernel.Plugins.OpenApi;
 
 /// <summary>
 /// Options for OpenAPI document parser.
 /// </summary>
+[Experimental("SKEXP0040")]
 public sealed class OpenApiDocumentParserOptions
 {
     /// <summary>

dotnet/src/Functions/Functions.OpenApi/OpenApi/OpenApiDocumentParserOptions.cs

@@ -1,12 +1,14 @@
 // Copyright (c) Microsoft. All rights reserved.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Microsoft.SemanticKernel.Plugins.OpenApi;
 
 /// <summary>
 /// Represents the context for an operation selection predicate.
 /// </summary>
+[Experimental("SKEXP0040")]
 public readonly struct OperationSelectionPredicateContext : IEquatable<OperationSelectionPredicateContext>
 {
     /// <summary>