### Description
This PR allows WebGPU EP to be built with Emscripten for WebAssembly,
Including:
- cmake build files update to support correct setup for Emscripten.
- code changes to fix build breaks for wasm
- change in Web CI pipeline to add a build-only target for wasm with
`--use_webgpu`.
### Description
Fixes build when specify with flag `--target
onnxruntime_providers_webgpu`
Otherwise the following error will occur:
```
range.cc
D:\code\onnxruntime\build\Windows\Debug\_deps\onnx-src\onnx\onnx_pb.h(65,10): error C1083: Cannot open include file: 'o
nnx/onnx-ml.pb.h': No such file or directory [D:\code\onnxruntime\build\Windows\Debug\onnxruntime_providers_webgpu.vcxp
roj]
(compiling source file '../../../onnxruntime/core/providers/webgpu/math/binary_elementwise_ops.cc')
```
### Description
This change fixes the DLL delay load problem for the WebGPU EP and
DirectML EP. See detailed explanation below.
### Problem
When onnxruntime.dll uses delay loading for its dependencies, the
dependencies are loaded using `LoadLibraryEx()`, which search the
directory of process (.exe) instead of this library (onnxruntime.dll).
This is a problem for usages of Node.js binding and python binding,
because Windows will try to find the dependencies in the directory of
node.exe or python.exe, which is not the directory of onnxruntime.dll.
There was previous attempt to fix this by loading DirectML.dll in the
initialization of onnxruntime nodejs binding, which works for DML EP but
is not a good solution because it does not really "delay" the load.
For WebGPU, the situation became worse because webgpu_dawn.dll depends
on dxil.dll and dxcompiler.dll, which are explicitly dynamically loaded
in the code using `LoadLibraryA()`. This has the same problem of the DLL
search.
### Solutions
For onnxruntime.dll loading its direct dependencies, it can be resolved
by set the [`__pfnDliNotifyHook2`
hook](https://learn.microsoft.com/en-us/cpp/build/reference/understanding-the-helper-function?view=msvc-170#structure-and-constant-definitions)
to load from an absolute path that constructed from the onnxruntime.dll
folder and the DLL name.
For webgpu_dawn.dll loading dxil.dll and dxcompiler.dll, since they are
explicitly loaded in the code, the hook does not work. Instead, it can
be resolved by ~~using WIN32 API `SetDllDirectory()` to add the
onnxruntime.dll folder to the search path.~~ preloading the 2 DLLs from
the onnxruntime.dll folder .
### Description
This change introduces the WebGPU EP into ONNX Runtime.
To make the PR as simple as possible, this PR excluded the following:
- C API changes for WebGPU EP
- actual implementation of WebGPU EP. Currently in this PR, WebGPU is a
stub implementation that does not register any kernel.
- Python IO Binding update
- Node.js IO Binding update
This PR now contains only 43 file changes (while the working branch
contains 130+) and hopefully this makes it easier to review.
There is going to be separated PRs for each mentioned above.
Current working branch: #21904
