Expose options for making schema generation conformant with the subset accepted by OpenAI.

[eiriktsarpalis]

Makes the following changes:

• Exposes additional configuration settings in the built-in schema generator making it conformant with OpenAI constraints.
• Adds a SchemaCreateOptions property to the AIFunctionFactoryCreateOptions class for controlling schema generation in AIFunctionFactory.
• Defaults AIFunctionFactory to using configuration that is conformant with OpenAI restrictions.

Fix #5612.

Microsoft Reviewers: Open in CodeFlow

[stephentoub]

Thanks

[eerhardt]

FYI - this introduces new trim/AOT warnings. I'm enabling the CI check in #5622.

    D:\git\extensions\src\Libraries\Microsoft.Extensions.AI.Abstractions\Utilities\AIJsonUtilities.Schema.cs(305): Trim analysis error IL2026: Microsoft.Extensions.AI.AIJsonUtilities.<>c__DisplayClass15_0.<GetJsonSchemaCore>g__TransformSchemaNode|0(JsonSchemaExporterContext,JsonNode): Using member 'System.Text.Json.Nodes.JsonArray.Add<String>(String)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Creating JsonValue instances with non-primitive types is not compatible with trimming. It can result in non-primitive types being serialized, which may have their members trimmed. [D:\git\extensions\test\Libraries\Microsoft.Extensions.AotCompatibility.TestApp\Microsoft.Extensions.AotCompatibility.TestApp.csproj]
    D:\git\extensions\src\Libraries\Microsoft.Extensions.AI.Abstractions\Utilities\AIJsonUtilities.Schema.cs(305): AOT analysis error IL3050: Microsoft.Extensions.AI.AIJsonUtilities.<>c__DisplayClass15_0.<GetJsonSchemaCore>g__TransformSchemaNode|0(JsonSchemaExporterContext,JsonNode): Using member 'System.Text.Json.Nodes.JsonArray.Add<String>(String)' which has 'RequiresDynamicCodeAttribute' can break functionality when AOT compiling. Creating JsonValue instances with non-primitive types requires generating code at runtime. [D:\git\extensions\test\Libraries\Microsoft.Extensions.AotCompatibility.TestApp\Microsoft.Extensions.AotCompatibility.TestApp.csproj]

I've opened #5626 for this.