Allow simpler input and outputs

[SirLynix]

Currently, a struct has to be used to specify inputs and outputs.

[nzsl_version("1.1")]
module;

const vertPos = array[vec2[f32]](
	vec2[f32](-1.0, -3.0),
	vec2[f32](-1.0, 1.0),
	vec2[f32]( 3.0, 1.0)
);

struct Input
{
    [builtin(vertex_index)] vert_index: i32
}

struct Output
{
    [builtin(position)] pos: vec4[f32] 
}

[entry(vert)]
fn main(input: Input) -> Output
{
    let output: Output;
    output.pos = vec4[f32](position, 0.0, 1.0);

    return output;
}

To simplify code we could allow some simpler syntax, perhaps something like

[entry(vert)]
fn main(vert_index: i32 @vertex_index) -> vec4[f32] @position 
{
    return vec4[f32](position, 0.0, 1.0);
}

However this syntax is pretty heavy and will make the parser/AST more complex to support attributes on parameters and return type, does anyone have a better idea?

[Kbz-8]

I see nothing wrong with the struct input being the only solution, I think it's a good practice.