Sync up with current WebGPU spec to allow FS input being a
subset of VS output instead of requiring a strict match.
This patch involves changing the validation and adding tests,
together with using the TruncateInterstageVariables for hlsl
generator to workaround the extra limit for D3D12 backend.
Bug: dawn:1493
Change-Id: I2d4ba7f43dbe57f17ecd5c5d659f4ca93bb682a3
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/109460
Commit-Queue: Shrek Shao <shrekshao@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Auto-Submit: Shrek Shao <shrekshao@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>