[js/webgpu] Fix shader compilation errors in cumsum (#18779)
### Description
This PR fixes below shader compilation errors:
```
Tint WGSL reader failure: :39:31 error: no matching overload for operator + (f32, i32)
5 candidate operators:
operator + (T, T) -> T where: T is abstract-float, abstract-int, f32, i32, u32 or f16
operator + (vecN<T>, T) -> vecN<T> where: T is abstract-float, abstract-int, f32, i32, u32 or f16
operator + (T, vecN<T>) -> vecN<T> where: T is abstract-float, abstract-int, f32, i32, u32 or f16
operator + (vecN<T>, vecN<T>) -> vecN<T> where: T is abstract-float, abstract-int, f32, i32, u32 or f16
operator + (matNxM<T>, matNxM<T>) -> matNxM<T> where: T is abstract-float, f32 or f16
sum = sum + get_inputByIndices(inputIndices);
^
- While validating [ShaderModuleDescriptor "CumSum"]
- While calling [Device].CreateShaderModule([ShaderModuleDescriptor "CumSum"]).