[WebGPU] allow WGSL template generation (#25130)
### Description
This PR introduces the
[WGSL-Template](https://github.com/fs-eire/wgsl-template) into WebGPU EP
to enable the capability of template based WGSL source generation.
The purpose of this change is to improve the readability of the WGSL
source code and reduce the future maintenance cost due to the difficulty
of understanding the current WGSL code generation logic.
### Explanation
- build
- for static code generator: `--use_webgpu`
- for dynamic code generator: `--use_webgpu --use_wgsl_template dynamic`
- the template files use extension `.wgsl.template` and are located in
`core/providers/webgpu/` folder.
- the corresponding C++ file should use
`shader_helper.ApplyTemplate<...>()` to apply the template. (check
pad.cc for example)
- for documentation - https://github.com/fs-eire/wgsl-template
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