Fix Metal crash on Intel Mac AMD GPU (missing setArgumentBuffer)

[wendlinga]

Problem

On macOS 11+, all GPUs are reported as Metal Argument Buffers Tier 2.
The MetalDescriptorSet constructor therefore skips calling
setArgumentBuffer() on the argument encoder when
useArgumentBuffersTier2 = true. However, when setDescriptor() later
calls argumentEncoder->setBuffer(...) for a DataTypePointer binding,
the AMD driver crashes because the encoder has no backing buffer:

-[BronzeMtlIndirectArgumentBufferEncoder setBuffer:offset:atIndex:] + 44
plume::MetalDescriptorSet::setDescriptor(...)

Crash observed on: Intel MacBook Pro, AMD Radeon 555X (AMDMTLBronzeDriver),
macOS 15.7.4.

Fix

In the DataTypePointer case of setDescriptor, call setArgumentBuffer()
before setBuffer() when useDirectBufferAddresses is false (i.e. not on
Metal3 hardware). This gives the encoder a valid backing buffer before any
encode operations:

argumentBuffer.argumentEncoder->setArgumentBuffer(argumentBuffer.mtl,
                                                  argumentBuffer.offset);
argumentBuffer.argumentEncoder->setBuffer(nativeBuffer,
                                          bufferDescriptor->offset,
                                          argumentIndex);

Impact

• Intel Mac AMD (useArgumentBuffersTier2 = true, useDirectBufferAddresses = false): crash eliminated.
• Apple Silicon / Metal3 (useDirectBufferAddresses = true): takes the direct GPU-address path as before — no change.
• Tier1 devices (useArgumentBuffersTier2 = false): setArgumentBuffer is already called in the constructor; this path is unchanged.