.Net: Removed experimental flags in Filters (#9774)

### Motivation and Context

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Closes: #9499

1. Removed `Experimental` flag from `AutoFunctionInvocationFilter`
classes and properties.
2. Removed `Experimental` flag from `IsStreaming` boolean property in
filter context models.
3. Added a unit test to verify function sequence index property
behavior.

### Contribution Checklist

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

- [x] The code builds clean without any errors or warnings
- [x] 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
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

dotnet/src/Connectors/Connectors.OpenAI.UnitTests/Core/AutoFunctionInvocationFilterTests.cs

@@ -78,6 +78,41 @@ public async Task FiltersAreExecutedCorrectlyAsync()
         Assert.Equal("Test chat response", result.ToString());
     }
 
+    [Fact]
+    public async Task FunctionSequenceIndexIsCorrectForConcurrentCallsAsync()
+    {
+        // Arrange
+        List<int> functionSequenceNumbers = [];
+        List<int> expectedFunctionSequenceNumbers = [0, 1, 0, 1];
+
+        var function1 = KernelFunctionFactory.CreateFromMethod((string parameter) => { return parameter; }, "Function1");
+        var function2 = KernelFunctionFactory.CreateFromMethod((string parameter) => { return parameter; }, "Function2");
+
+        var plugin = KernelPluginFactory.CreateFromFunctions("MyPlugin", [function1, function2]);
+
+        var kernel = this.GetKernelWithFilter(plugin, async (context, next) =>
+        {
+            functionSequenceNumbers.Add(context.FunctionSequenceIndex);
+
+            await next(context);
+        });
+
+        this._messageHandlerStub.ResponsesToReturn = GetFunctionCallingResponses();
+
+        // Act
+        var result = await kernel.InvokePromptAsync("Test prompt", new(new OpenAIPromptExecutionSettings
+        {
+            FunctionChoiceBehavior = FunctionChoiceBehavior.Auto(options: new()
+            {
+                AllowParallelCalls = true,
+                AllowConcurrentInvocation = true
+            })
+        }));
+
+        // Assert
+        Assert.Equal(expectedFunctionSequenceNumbers, functionSequenceNumbers);
+    }
+
     [Fact]
     public async Task FiltersAreExecutedCorrectlyOnStreamingAsync()
     {

dotnet/src/SemanticKernel.Abstractions/Filters/AutoFunctionInvocation/AutoFunctionInvocationContext.cs

@@ -1,6 +1,5 @@
 // Copyright (c) Microsoft. All rights reserved.
 
-using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 using Microsoft.SemanticKernel.ChatCompletion;
 
@@ -9,7 +8,6 @@ namespace Microsoft.SemanticKernel;
 /// <summary>
 /// Class with data related to automatic function invocation.
 /// </summary>
-[Experimental("SKEXP0001")]
 public class AutoFunctionInvocationContext
 {
     /// <summary>

dotnet/src/SemanticKernel.Abstractions/Filters/AutoFunctionInvocation/IAutoFunctionInvocationFilter.cs

@@ -1,7 +1,6 @@
 // Copyright (c) Microsoft. All rights reserved.
 
 using System;
-using System.Diagnostics.CodeAnalysis;
 using System.Threading.Tasks;
 
 namespace Microsoft.SemanticKernel;
@@ -11,7 +10,6 @@ namespace Microsoft.SemanticKernel;
 /// <summary>
 /// Interface for filtering actions during automatic function invocation.
 /// </summary>
-[Experimental("SKEXP0001")]
 public interface IAutoFunctionInvocationFilter
 {
     /// <summary>

dotnet/src/SemanticKernel.Abstractions/Filters/Function/FunctionInvocationContext.cs

@@ -1,6 +1,5 @@
 // Copyright (c) Microsoft. All rights reserved.
 
-using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 
 namespace Microsoft.SemanticKernel;
@@ -38,7 +37,6 @@ internal FunctionInvocationContext(Kernel kernel, KernelFunction function, Kerne
     /// <summary>
     /// Boolean flag which indicates whether a filter is invoked within streaming or non-streaming mode.
     /// </summary>
-    [Experimental("SKEXP0001")]
     public bool IsStreaming { get; init; }
 
     /// <summary>

dotnet/src/SemanticKernel.Abstractions/Filters/Prompt/PromptRenderContext.cs

@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft. All rights reserved.
 
-using System.Diagnostics.CodeAnalysis;
 using System.Threading;
+
 namespace Microsoft.SemanticKernel;
 
 /// <summary>
@@ -37,7 +37,6 @@ internal PromptRenderContext(Kernel kernel, KernelFunction function, KernelArgum
     /// <summary>
     /// Boolean flag which indicates whether a filter is invoked within streaming or non-streaming mode.
     /// </summary>
-    [Experimental("SKEXP0001")]
     public bool IsStreaming { get; init; }
 
     /// <summary>

dotnet/src/SemanticKernel.Abstractions/Kernel.cs

@@ -144,7 +144,6 @@ public Kernel Clone() =>
     /// <summary>
     /// Gets the collection of auto function invocation filters available through the kernel.
     /// </summary>
-    [Experimental("SKEXP0001")]
     public IList<IAutoFunctionInvocationFilter> AutoFunctionInvocationFilters =>
         this._autoFunctionInvocationFilters ??
         Interlocked.CompareExchange(ref this._autoFunctionInvocationFilters, [], null) ??