[webgpu] Use i32 as coords type in WGSL

[axinging]

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[axinging]

@qjia7 @haoyunfeix @xhcao @gyagp PTAL

A comment, we can use

1. getXXXAtOutCoordsByGlobalId(vec3(globalId), index) to get data.
2. Or we can define an extra globalIdInt:

let globalId = vec3<i32>globalIdU32;

Then use getXXXAtOutCoordsByGlobalId(globalId , index) to get data.

As to the option 1, it will save a vec3 in each program. As to the option 2, it will save some code changes. Current 1 is applied.

[qjia7]

I vote keeping globalId, localId's type as function parameter types. And do the corresponding cast as needed. And for others, we all unify to use i32 instead of u32 expect for dispatchSize. DispatchSize or numWorkGroups is similarly like globalId, localId which is u32 instead i32.

[qjia7]

Looks better, thanks. LGTM with two nits.

[lina128]

Thank you for the refactor, looks great!

Reviewable status: complete! 2 of 1 approvals obtained (waiting on @axinging and @pyu10055)