[Event Hubs] Update the create and send batch as per feedback

[ShivangiReja]

This PR updates the following:

• Throws error Partition key is not supported when using producers that were created using a partition id when creating batch instead of send()
• Added variable count and getter for count in EventDataBatch which returns number of events in the batch
• Change size -> sizeInBytes in EventDataBatch
• In normal case of send(), if an empty array is passed in, exit without any error.

For more details: #4307, #4302

[ramya-rao-a]

Now that we have count exposed on the batch, maybe we should check the count instead of !eventData.batchMessage. We can also initialize the eventData.batchMessage to an empty Buffer in the constructor for EventDataBatch and remove the undefined from its type. That way no one ever has to check for !eventData.batchMessage.

Thoguhts?

[ShivangiReja]

Now that we have count exposed on the batch, maybe we should check the count instead of !eventData.batchMessage.

Agreed!

We can also initialize the eventData.batchMessage to an empty Buffer in the constructor for EventDataBatch and remove the undefined from its type

It will not add any extra value, right?

[ramya-rao-a]

The extra value is that we dont have to check for if (eventData.batchMessage) or use eventData.batchMessage! before using that property

[ShivangiReja]

If we initialize batchMessage = Buffer.alloc(); in the EventDataBatch constructor, It will create a new buffer object of the specified size(in our case empty Buffer object).

Buffer object will use memory, so my point was why waste memory? If It is not adding any extra value other than this check if (eventData.batchMessage) or eventData.batchMessage!

[ramya-rao-a]

sounds good

[ramya-rao-a]

There are some merge conflicts here, can you take a look?