Support output groups

[donmccurdy]

In the current implementation, if the end-user wants to load different models on desktop and mobile, they have to provide both models as inputs. Processing on each (if it needs to be different) would then be configured with the plugin's include flag, like include: "**/*.mobile.glb".

Alternatively, it could be interesting to explore having the plugin generate multiple groups of outputs, each with different optimization settings, like...

const DEFAULTS = [ mozjpeg(), oxipng() ];

export default defineConfig({
  // ...
  plugins: [
    gltf({
      output: [
        { name: 'hi', transforms: [ textureResize({size: [2048, 2048]}), ...DEFAULTS ] },
        { name: 'lo', transforms: [ textureResize({size: [1024, 1024]}), ...DEFAULTS ] },
      ]
    });
  ]
});

... and then the application might choose which to import based on device type or other considerations:

import { lo, hi } from 'path/to/content.glb';

export const models = [
  // NOTE: Example only. 'prefers-reduced-data' is not widely supported.
  { name: 'content', type: 'glb', url: matchMedia('prefers-reduced-data') ? lo : hi }
];

[juniorxsound]

This would be incredibly neat! Got me thinking of how nicely this could integrate into things like THREE.LOD.