[ggml-webgpu] Handle buffer overlap / buffer aliasing for concat operator

[nikhilJain17]

Overview

While testing the WebGPU backend with stable-diffusion.cpp, I encountered the following error:

Device error! Reason: 2, Message: Writable storage buffer binding aliasing found between [BindGroup "concat_f32"] 
set at bind group index 0, binding index 0, and [BindGroup "concat_f32"] set at bind group index 0, binding index 1, 
with overlapping ranges (offset: 2924288, size: 1310720) and (offset: 2924288, size: 1310720) in [Buffer "tensor_buf2"].

Since WebGPU does not allow a read bind and a write bind on the same buffer, there was a workaround to merge two overlapping src buffers into a merged_src buffer in #22456. This diff applies the same technique to the concat shader.

cc @yomaytk

Requirements

• I have read and agree with the contributing guidelines
• AI usage disclosure: Yes, to root cause the issue and fix a git issue.

[yomaytk]

Hi @nikhilJain17, thanks for working on this, and it all looks great! LGTM

[CISC]

Deja-vú. :)