feat: Shell-less entry function wrappers

This depends on #1835 being done, but I was wondering how viable it would be to allow for a workflow where entry functions can still be defined separately from the render pipeline, yet benefit from not having to setup a shell.

const vertex = tgpu.vertexFn(({ $vertexIndex }) => {
  'use gpu';
  const pos = [
    d.vec2f(0.0, 0.5),
    d.vec2f(-0.5, -0.5),
    d.vec2f(0.5, -0.5),
  ];

  const uv = [
    d.vec2f(0.5, 1.0),
    d.vec2f(0.0, 0.0),
    d.vec2f(1.0, 0.0),
  ];

  return {
    $position: d.vec4f(pos[$vertexIndex], 0, 1),
    uv: uv[$vertexIndex],
  };
});

const fragment = tgpu.fragmentFn<typeof vertexFn>(({ uv }) => {
  'use gpu';
  return getGradientColor((uv.x + uv.y) / 2);
});

const pipeline = root.createRenderPipeline({ vertex, fragment });

I'm not yet sure how attribute type information would be provided to a vertex function, but we can figure that out while prototyping this feature.

Start by reading the prerequisite issue #1835, then prototype the separate vertexFn and fragmentFn entry functions shown in this issue. Done means entry functions can be passed directly to createRenderPipeline without a shell, with a decided approach for providing vertex attribute type information.