TSL: Fix WGSL Functions using wrong type

[RenaudRohlinger]

Related issue: #28669

Description

We just fixed the types of properties for WGSL functions, the type of declaration needed the same treatment.

Example:

const a = tslFn( ( [] ) => {

return ivec2();

}).setLayout({ type: 'ivec2', ... })

const b = uniforms([], 'ivec4')

// Later in the shader:
const c = a().x.add(b.x)

// ----- Transpilation ------
// Before this PR, some operations were casting some nodes to float:
const c = a().x.add( float( vec4<i32>(b).x ) ) // <-- breaks because int32 + float32


// After this PR
const c = a().x.add( vec4<i32>(b).x ) // <-- works because int32 + int32

This contribution is funded by Utsubo

[sunag]

@RenaudRohlinger I moved outputType into the parser because it is an immutable value.