Support integer discriminators in OpenAPI polymorphism

Added support for integer type discriminators in OpenAPI schema generation for polymorphic types. Discriminator property type, value, and default are now set dynamically based on the discriminator's type (string or integer). The discriminator property name is consistently determined and defaults to "$type" if unspecified.

Author: icnocop

src/SignalR.OpenApi/Generation/SignalROpenApiDocumentGenerator.cs

@@ -723,9 +723,17 @@ private void AddPolymorphicSubEndpoints(
             return;
         }
 
+        var discriminatorPropertyName = polymorphicAttr.TypeDiscriminatorPropertyName ?? "$type";
+
         foreach (var derived in derivedTypes)
         {
-            var discriminatorValue = derived.TypeDiscriminator as string;
+            var discriminatorValue = derived.TypeDiscriminator switch
+            {
+                string s => s,
+                int i => i.ToString(System.Globalization.CultureInfo.InvariantCulture),
+                _ => null,
+            };
+
             if (discriminatorValue is null)
             {
                 continue;
@@ -736,11 +744,15 @@ private void AddPolymorphicSubEndpoints(
 
             // Add the discriminator property as a read-only constant.
             derivedSchema.Properties ??= new Dictionary<string, OpenApiSchema>();
-            derivedSchema.Properties[polymorphicAttr.TypeDiscriminatorPropertyName] = new OpenApiSchema
+            derivedSchema.Properties[discriminatorPropertyName] = new OpenApiSchema
             {
-                Type = "string",
-                Enum = [new Microsoft.OpenApi.Any.OpenApiString(discriminatorValue)],
-                Default = new Microsoft.OpenApi.Any.OpenApiString(discriminatorValue),
+                Type = derived.TypeDiscriminator is string ? "string" : "integer",
+                Enum = derived.TypeDiscriminator is string
+                    ? [new Microsoft.OpenApi.Any.OpenApiString(discriminatorValue)]
+                    : [new Microsoft.OpenApi.Any.OpenApiInteger(int.Parse(discriminatorValue, System.Globalization.CultureInfo.InvariantCulture))],
+                Default = derived.TypeDiscriminator is string
+                    ? new Microsoft.OpenApi.Any.OpenApiString(discriminatorValue)
+                    : new Microsoft.OpenApi.Any.OpenApiInteger(int.Parse(discriminatorValue, System.Globalization.CultureInfo.InvariantCulture)),
                 ReadOnly = true,
             };
 
@@ -784,7 +796,7 @@ private void AddPolymorphicSubEndpoints(
                 isClientEvent: false,
                 parameterCount: 1,
                 flattenedBody: true,
-                discriminatorProperty: polymorphicAttr.TypeDiscriminatorPropertyName,
+                discriminatorProperty: discriminatorPropertyName,
                 discriminatorValue: discriminatorValue);
 
             document.Paths[subPathKey] = new OpenApiPathItem