Deprecate -sUSE_WEBGPU in favor of Dawn's emdawnwebgpu

Adds a linker warning for using -sUSE_WEBGPU, and update documentation.

Emscripten's implementation of webgpu.h is unmaintained. We want people
to move to Dawn's emdawnwebgpu implementation (fork). However, the API
has changed substantially, so this not a clean transition. Plus, there
might be new bugs in that implementation. So we need a decently long
deprecation period before removing the old implementation.

Issue: 23432

Author: kainino0x

site/source/docs/tools_reference/settings_reference.rst

@@ -880,7 +880,13 @@ Default value: false
 USE_WEBGPU
 ==========
 
-Enables support for WebGPU (via "webgpu/webgpu.h").
+Enables the built-in implementation of ``<webgpu/webgpu.h>``.
+Deprecated: Please try migrating to "emdawnwebgpu", a fork maintained by Dawn
+(but still cross-browser) that implements a newer, more stable version of
+the standardized interface, and file feedback (see its package README).
+https://github.com/google/dawn/releases
+
+.. note:: This setting is deprecated
 
 Default value: false
 

src/settings.js

@@ -572,8 +572,14 @@ var GL_FFP_ONLY = false;
 // [link]
 var GL_PREINITIALIZED_CONTEXT = false;
 
-// Enables support for WebGPU (via "webgpu/webgpu.h").
+// Enables the built-in implementation of ``<webgpu/webgpu.h>``.
+// Deprecated: Please try migrating to ``--use-port=contrib.emdawnwebgpu``
+// which uses a fork maintained by Dawn (but still cross-browser) that
+// implements a newer, more stable version of the standardized interface. If
+// you find issues, verify it in the latest nightly release
+// (https://github.com/google/dawn/releases) and file feedback with Dawn.
 // [link]
+// [deprecated]
 var USE_WEBGPU = false;
 
 // Enables building of stb-image, a tiny public-domain library for decoding

test/test_other.py

@@ -10259,6 +10259,7 @@ def test_closure_webgpu(self):
     self.build('hello_world.c', emcc_args=[
       '--closure=1',
       '-Werror=closure',
+      '-Wno-error=deprecated',
       '-sINCLUDE_FULL_LIBRARY',
       '-sUSE_WEBGPU',
     ])

tools/settings.py

@@ -125,6 +125,7 @@
     'LEGALIZE_JS_FFI': 'to disable JS type legalization use `-sWASM_BIGINT` or `-sSTANDALONE_WASM`',
     'ASYNCIFY_EXPORTS': 'please use JSPI_EXPORTS instead',
     'MAYBE_WASM2JS': 'lack of usage',
+    'USE_WEBGPU': 'please try migrating to --use-port=contrib.emdawnwebgpu, which uses a fork maintained by Dawn (but still cross-browser) that implements a newer, more stable version of the standardized interface. If you find issues, verify it in the latest nightly release (https://github.com/google/dawn/releases) and file feedback with Dawn.',
 }
 
 # Settings that don't need to be externalized when serializing to json because they