Deprecate -sUSE_WEBGPU in favor of --use-port=emdawnwebgpu

[kainino0x]

Add a linker warning for using -sUSE_WEBGPU pointing to --use-port=emdawnwebgpu, and update documentation.

Moves the port from contrib.emdawnwebgpu to just emdawnwebgpu since we'll keep maintaining it as we work on Emdawnwebgpu.

Emscripten's implementation of webgpu.h is unmaintained. Dawn now maintains "emdawnwebgpu", a fork of Emscripten's implementation that is up to date, resolving #23432.

We want people to move to emdawnwebgpu. However, the API has changed substantially, so it will take people time to switch over. Plus, there might be new bugs in that implementation. So we need a decently long deprecation period before removing the old implementation.

Closes #23432
Starts fixing #24265

[xpenatan]

Hi, what about firefox or browsers that dont use dawn?

[kainino0x]

emdawnwebgpu is independent of browser (except it supports a few experimental features that are only in Chromium browsers). They're actually just a fork of the bindings currently in Emscripten, the only difference is we're maintaining them in the Dawn repository instead of here.

I should clarify this in the deprecation message and/or in the emdawnwebgpu docs.

[sbc100]

I think we should maybe wait until we have a way for folks to do --use-port=contrib/emdawn.py (or something like that) to use the new version. i.e. lets fix #24260 first?

[ypujante]

I think we should maybe wait until we have a way for folks to do --use-port=contrib/emdawn.py (or something like that) to use the new version. i.e. lets fix #24260 first?

I agree 100%. It would be better to deprecate -sUSE_WEBGPU while offering an alternative that is as painless as possible. And using the --user-port=contrib.emdawn syntax would be the least painless possible...

[kainino0x]

Seems reasonable.

[sbc100]

Can you add a ChangeLog entry?