Add a mode to the receive buffer to handle external buffers

[guhetier]

Description

As part of #4747, the receive buffer needs a mode to operate on buffers provided by the application.
This PR defines a new QUIC_RECV_BUF_MODE_EXTERNAL mode.

• QUIC_RECV_CHUNKs now have a pointer to the actual buffer instead of an end-of-struct array
  • Except for the EXTERNAL mode, the buffer is still part of the same allocation as the chunk
  • For EXTERNAL mode, buffers are provided by the application and chunks point to them
• The EXTERNAL mode writes only once to the provided buffers and discard them when they are drained. Buffers are never re-used.
• Reads and writes can span through multiple chunks. They are never treated as circular buffers.
• The EXTERNAL mode never allocates / re-allocate buffers
  • The virtual buffer size is set to the sum of the provided buffer sizes to avoid receiving more data than we can buffer
  • The virtual buffer size can now decrease when data is drained - but the maximum byte offset that can be received still only increases.

Testing

Unit tests have been added

Documentation

To be done

[nibanks]

Somewhat independent of this PR, I am wondering if we could/should annotate this pointer:

Suggested change

	uint8_t *Buffer; // Pointer to the buffer itself. Doesn't need to be freed independently:
	_Field_size_bytes_(AllocLength)
	uint8_t *Buffer; // Pointer to the buffer itself. Doesn't need to be freed independently:

[nibanks]

Maybe improve the annotation a bit more? I think this is it:

Suggested change

	_In_ uint8_t* Buffer
	_In_updates_(AllocLength) uint8_t* Buffer

[guhetier]

Yes. I also need to add the corresponding annotations on the chunk struct itself.

[nibanks]

FYI, our style capitalizes all variables and fields.

Suggested change

	uint64_t rangeMax;
	uint64_t RangeMax;

Please update for everything else too. Thanks!

[nibanks]

FYI, we also have CXPLAT_DBG_ASSERTMSG which could be used here instead of the comment:

Suggested change

	CXPLAT_DBG_ASSERT(RecvBuffer->RecvMode != QUIC_RECV_BUF_MODE_EXTERNAL); // Should never resize in external mode
	CXPLAT_DBG_ASSERTMSG(RecvBuffer->RecvMode != QUIC_RECV_BUF_MODE_EXTERNAL, "Should never resize in external mode");

But you don't have to use it. We don't use it that much.

[nibanks]

Suggested change

	// This is skiped in external mode since the entire virtual length is
	// This is skipped in external mode since the entire virtual length is

[nibanks]

style nit:

Suggested change

	for (uint32_t i = 0; i < *BufferCount && remainingDataToRead > 0; ++i)
	{
	for (uint32_t i = 0; i < *BufferCount && remainingDataToRead > 0; ++i) {