bug: WGSL-implemented entry function args can shadow local definitions

The following WGSL-implemented vertex function:

const mainVertex = tgpu.vertexFn({
  in: { vi: d.builtin.vertexIndex },
  out: { outPos: d.builtin.position },
})(/* wgsl */ `{
  var pos = array<vec2f, 3>(
    vec2(0.0, 0.5),
    vec2(-0.5, -0.5),
    vec2(0.5, -0.5)
  );

  var vi = in.vi;

  return Out(vec4f(pos[in.vertexIndex], 0.0, 1.0));
}`);

Currently generates the following WGSL:

struct mainVertex_Output {
  @builtin(position) outPos: vec4f,
}

@vertex fn mainVertex(@builtin(vertex_index) vi: u32) -> mainVertex_Output {
  var pos = array<vec2f, 3>(
    vec2(0.0, 0.5),
    vec2(-0.5, -0.5),
    vec2(0.5, -0.5)
  );

  var vi = vi;

  return mainVertex_Output(vec4f(pos[in.vertexIndex], 0.0, 1.0));
}

Notice the var vi = vi line.

Reproduce the issue with the provided TypeScript vertexFn example and inspect the generated WGSL around the entry-function parameters and local definitions. The fix is complete when an entry argument and a local declaration with the same name no longer produce a self-shadowing assignment such as var vi = vi; verify the generated shader remains valid.