.Net: Fix mapping of the KernelParameterMetadata.IsRequired property (microsoft#11309)

### Motivation, Context and Description

This PR fixes the issue caused by accessing the `required` property
value as if it were a boolean property, instead of accessing it as an
array of strings. Additionally, it reads the `required` property from
the object root instead of reading it from each individual property of
the object because the `required` property is defined at the root level
to specify which properties are mandatory for the entire object.

So, when iterating over the object root level properties, the code now
uses the `"required": ["options"]` property declared at the root level
instead of the `"required": ["outputPath"]` declared at the `options`
property level.
```json
{
    "type": "object",
    "properties": {
        "options": {
            "type": "object",
            "description": "Code generation options",
            "properties": {
                "outputPath": {
                    "type": "string",
                    "description": "Directory path where generated tests will be saved (use absolute path)"
                },
                "testNamePrefix": {
                    "type": "string",
                    "description": "Prefix to use for generated test names (default: \u0027GeneratedTest\u0027)"
                },
                "includeComments": {
                    "type": "boolean",
                    "description": "Whether to include descriptive comments in generated tests"
                }
            },
            "required": [
                "outputPath"
            ]
        }
    },
    "required": [
        "options"
    ]
}
```
JsonSpec:
https://json-schema.org/understanding-json-schema/reference/object#required
Fixes: microsoft#11292
Contributes to:
microsoft#11212

Author: SergeyMenshykh

dotnet/src/SemanticKernel.Abstractions/AI/ChatCompletion/AIFunctionKernelFunction.cs

@@ -66,6 +66,8 @@ private static IReadOnlyList<KernelParameterMetadata> MapParameterMetadata(AIFun
             return Array.Empty<KernelParameterMetadata>();
         }
 
+        HashSet<string>? requiredParameters = GetRequiredParameterNames(aiFunction.JsonSchema);
+
         List<KernelParameterMetadata> kernelParams = [];
         var parameterInfos = aiFunction.UnderlyingMethod?.GetParameters().ToDictionary(p => p.Name!, StringComparer.Ordinal);
         foreach (var param in properties.EnumerateObject())
@@ -76,7 +78,7 @@ private static IReadOnlyList<KernelParameterMetadata> MapParameterMetadata(AIFun
             {
                 Description = param.Value.TryGetProperty("description", out JsonElement description) ? description.GetString() : null,
                 DefaultValue = param.Value.TryGetProperty("default", out JsonElement defaultValue) ? defaultValue : null,
-                IsRequired = param.Value.TryGetProperty("required", out JsonElement required) && required.GetBoolean(),
+                IsRequired = requiredParameters?.Contains(param.Name) ?? false,
                 ParameterType = paramInfo?.ParameterType,
                 Schema = param.Value.TryGetProperty("schema", out JsonElement schema)
                     ? new KernelJsonSchema(schema)
@@ -86,4 +88,25 @@ private static IReadOnlyList<KernelParameterMetadata> MapParameterMetadata(AIFun
 
         return kernelParams;
     }
+
+    /// <summary>
+    /// Gets the names of the required parameters from the AI function's JSON schema.
+    /// </summary>
+    /// <param name="schema">The JSON schema of the AI function.</param>
+    /// <returns>The names of the required parameters.</returns>
+    private static HashSet<string>? GetRequiredParameterNames(JsonElement schema)
+    {
+        HashSet<string>? requiredParameterNames = null;
+
+        if (schema.TryGetProperty("required", out JsonElement requiredElement) && requiredElement.ValueKind == JsonValueKind.Array)
+        {
+            foreach (var node in requiredElement.EnumerateArray())
+            {
+                requiredParameterNames ??= [];
+                requiredParameterNames.Add(node.GetString()!);
+            }
+        }
+
+        return requiredParameterNames;
+    }
 }

dotnet/src/SemanticKernel.UnitTests/AI/ChatCompletion/AIFunctionKernelFunctionTests.cs

@@ -0,0 +1,28 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System.Linq;
+using Microsoft.Extensions.AI;
+using Microsoft.SemanticKernel;
+using Microsoft.SemanticKernel.ChatCompletion;
+using Xunit;
+
+namespace SemanticKernel.UnitTests.AI.ChatCompletion;
+
+public class AIFunctionKernelFunctionTests
+{
+    [Fact]
+    public void ShouldAssignIsRequiredParameterMetadataPropertyCorrectly()
+    {
+        // Arrange and Act
+        AIFunction aiFunction = AIFunctionFactory.Create((string p1, int? p2 = null) => p1);
+
+        AIFunctionKernelFunction sut = new(aiFunction);
+
+        // Assert
+        KernelParameterMetadata? p1Metadata = sut.Metadata.Parameters.FirstOrDefault(p => p.Name == "p1");
+        Assert.True(p1Metadata?.IsRequired);
+
+        KernelParameterMetadata? p2Metadata = sut.Metadata.Parameters.FirstOrDefault(p => p.Name == "p2");
+        Assert.False(p2Metadata?.IsRequired);
+    }
+}

dotnet/src/SemanticKernel.UnitTests/SemanticKernel.UnitTests.csproj

@@ -24,7 +24,7 @@
     </PackageReference>
     <PackageReference Include="Microsoft.ML.Tokenizers" />
     <PackageReference Include="Microsoft.Extensions.Logging.Console" />
-    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" />
+    <PackageReference Include="Microsoft.Extensions.AI" />
   </ItemGroup>
 
   <ItemGroup>