[C++][FlightRPC] Sending 0-length buffers to gRPC can result in indefinite hangs on MacOS/iOS platforms

### Describe the bug, including details regarding any error messages, version, and platform.

A [gRPC issue](https://github.com/grpc/grpc/pull/37255) has been identified where transmitting buffers of zero length leads to a persistent hang on MacOS/iOS platforms.

Such zero-length buffers may arise, for example, in the context of using the Array structure alongside a validity bitmap, as outlined in the [Arrow Spec](https://arrow.apache.org/docs/format/Columnar.html#validity-bitmaps).

Essentially, when every element within an Array is valid (i.e., not null), it's possible to represent this state with a null validity bitmap, indicating that all elements are valid. This scenario is realized through the use of a null buffer, as demonstrated here:
https://github.com/apache/arrow/blob/187197c369058f7d1377c1b161c469a9e4542caf/cpp/src/arrow/ipc/writer.cc#L165-L179


The relevant sections of code from both transport mechanisms are provided below for reference:
https://github.com/apache/arrow/blob/187197c369058f7d1377c1b161c469a9e4542caf/cpp/src/arrow/flight/transport/grpc/serialization_internal.cc#L283-L287

https://github.com/apache/arrow/blob/187197c369058f7d1377c1b161c469a9e4542caf/cpp/src/arrow/flight/transport/ucx/ucx_internal.cc#L590-L591

Upon examining the UCX transport's approach, it's evident that a precaution is taken to avoid sending zero-length buffers. This strategy appears prudent, as it eliminates the need to forward non-transmittable buffers to the transport layer, potentially offering a solution to the issue observed with gRPC.

### Component(s)

C++, FlightRPC

	// In V4, null types have no validity bitmap
	// In V5 and later, null and union types have no validity bitmap
	if (internal::HasValidityBitmap(arr.type_id(), options_.metadata_version)) {
	if (arr.null_count() > 0) {
	std::shared_ptr<Buffer> bitmap;
	RETURN_NOT_OK(GetTruncatedBitmap(arr.offset(), arr.length(), arr.null_bitmap(),
	options_.memory_pool, &bitmap));
	out_->body_buffers.emplace_back(std::move(bitmap));
	} else {
	// Push a dummy zero-length buffer, not to be copied
	out_->body_buffers.emplace_back(kNullBuffer);
	}
	}
	return VisitType(arr);
	}

	// Enqueue body buffers for writing, without copying
	for (const auto& buffer : ipc_msg.body_buffers) {
	// Buffer may be null when the row length is zero, or when all
	// entries are invalid.
	if (!buffer) continue;

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[C++][FlightRPC] Sending 0-length buffers to gRPC can result in indefinite hangs on MacOS/iOS platforms #43447

Describe the bug, including details regarding any error messages, version, and platform.

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	for (const auto& buffer : payload.ipc_message.body_buffers) {
	if (!buffer \|\| buffer->size() == 0) continue;