onnxruntime

d74a6b97 - Isolate bundled Dawn implementation from WebGPU context (#32964)

Isolate bundled Dawn implementation from WebGPU context (#32964) ## Summary The common WebGPU context handles both bundled and host-provided Dawn, but it also includes Dawn native/platform headers and implements the bundled worker pool. Move the implementation-dependent code into a bundled-only translation unit so that the common context no longer depends on `dawn::native` or `dawn::platform`. - Extract default proc-table lookup, custom-platform instance creation, and native adapter enumeration behind private typed helpers. - Exclude the bundled-only source from external-Dawn and Emscripten builds. - Preserve worker-pool sizing, platform lifetime, instance features, and adapter-selection behavior. No public API or packaging changes. ## Validation - Windows x64 Release, bundled Dawn: built `onnxruntime_provider_test`; ran `WebGpuContextTest.*`, with 27 passed and one expected skip (`AdapterIndexRejectsUnsupportedBuild`). This includes physical adapter selection and device operations. - Windows x64 Release, `--use_webgpu --use_external_dawn`: configured and built `onnxruntime_providers_webgpu`. The bundled-only translation unit is excluded from the generated project. - Scoped `lintrunner` and `git diff --cached --check` passed. External-host runtime and Emscripten execution were not tested locally.