Add schema loader

Author: MaggieKimani1

src/Microsoft.OpenApi/Reader/V31/OpenApiV31VersionService.cs

@@ -57,6 +57,7 @@ public OpenApiV31VersionService(OpenApiDiagnostic diagnostic)
             [typeof(OpenApiResponse)] = OpenApiV31Deserializer.LoadResponse,
             [typeof(OpenApiResponses)] = OpenApiV31Deserializer.LoadResponses,
             [typeof(JsonSchema)] = OpenApiV31Deserializer.LoadSchema,
+            [typeof(OpenApiSchema)] = OpenApiV31Deserializer.LoadOpenApiSchema,
             [typeof(OpenApiSecurityRequirement)] = OpenApiV31Deserializer.LoadSecurityRequirement,
             [typeof(OpenApiSecurityScheme)] = OpenApiV31Deserializer.LoadSecurityScheme,
             [typeof(OpenApiServer)] = OpenApiV31Deserializer.LoadServer,