WebGPU: set vertex buffers. This change actually sets the vertex attributes that are added to the render pipeline description owned by the context, as well as sets the vertex buffer in the pipeline. Bug: angleproject:359823692 Change-Id: I5e94b357a4e6eadc1bbba54965cef94f90113b4e Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5789155 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org> Reviewed-by: Liza Burakova <liza@chromium.org>