Avoid ServiceBus*Options allocations (#44885)

- Avoid allocating empty `ServiceBusClientOptions` and `ServiceBusProcessorOptions` instances when creating instances of `ServiceBusClient` and `ServiceBusProcessor`.
- Remove unused `ServiceBusSenderOptions.Clone()` method.

sdk/servicebus/Azure.Messaging.ServiceBus/src/Client/ServiceBusClient.cs

@@ -120,7 +120,7 @@ protected ServiceBusClient()
         /// Other values will be ignored; to configure the processor, please use the <see cref="ServiceBusClientOptions" />.
         /// </remarks>
         public ServiceBusClient(string connectionString) :
-            this(connectionString, new ServiceBusClientOptions())
+            this(connectionString, null as ServiceBusClientOptions)
         {
         }
 
@@ -192,7 +192,7 @@ public ServiceBusClient(
         /// This is likely to be similar to <c>{yournamespace}.servicebus.windows.net</c>.</param>
         /// <param name="credential">The Azure managed identity credential to use for authorization.  Access controls may be specified by the Service Bus namespace.</param>
         public ServiceBusClient(string fullyQualifiedNamespace, TokenCredential credential) :
-            this(fullyQualifiedNamespace, (object)credential, new ServiceBusClientOptions())
+            this(fullyQualifiedNamespace, (object)credential, null)
         {
         }
 
@@ -562,7 +562,7 @@ public virtual ServiceBusProcessor CreateProcessor(string queueName)
                 entityPath: queueName,
                 connection: Connection,
                 isSessionEntity: false,
-                options: new ServiceBusProcessorOptions());
+                options: null);
         }
 
         /// <summary>
@@ -619,7 +619,7 @@ public virtual ServiceBusProcessor CreateProcessor(
                 entityPath: EntityNameFormatter.FormatSubscriptionPath(topicName, subscriptionName),
                 connection: Connection,
                 isSessionEntity: false,
-                options: new ServiceBusProcessorOptions());
+                options: null);
         }
 
         /// <summary>

sdk/servicebus/Azure.Messaging.ServiceBus/src/Sender/ServiceBusSenderOptions.cs

@@ -44,16 +44,5 @@ public class ServiceBusSenderOptions
         ///
         [EditorBrowsable(EditorBrowsableState.Never)]
         public override string ToString() => base.ToString();
-
-        /// <summary>
-        /// Creates a new copy of the current <see cref="ServiceBusReceiverOptions" />, cloning its attributes into a new instance.
-        /// </summary>
-        ///
-        /// <returns>A new copy of <see cref="ServiceBusReceiverOptions" />.</returns>
-        internal ServiceBusSenderOptions Clone() =>
-            new ServiceBusSenderOptions
-            {
-                Identifier = Identifier
-            };
     }
 }